Telescope Sentence Examples

A telescope is like a very strong eye.

This angle, therefore, divided by the magnifying power of the telescope gives the real angular distance of the centres of a double star.

The improvement of the telescope was justly regarded as a sine qua non for the advancement of astronomical knowledge.

It has been found by Sir William Herschel and others that the definition of a telescope is often improved by stopping off a part of the central area of the object-glass; but the advantage to be obtained in this way is in no case great, and anything like a reduction of the aperture to a narrow annulus is attended by a development of the external luminous rings sufficient to outweigh any improvement due to the diminished diameter of the central area.'

He certainly describes a method of constructing a telescope, but not so as to lead one to conclude that he was in possession of that instrument.

The planets in question appeared in the telescope as star-like objects which could be compared with the stars with much greater accuracy than a planetary disk like that of Mars, the apparent form of which was changed by its varying phase, due to the different directions of the sun's illumination.

Yerkes telescope, is shown in figs.

Here stands the Royal Observatory, in which the great Dunecht telescope was erected in 1896.

The eye, unaided or armed with a telescope, is able to see, as points of light, stars subtending no sentsible angle.

Talbot ascribes the appearance to diffraction; and he recommends the use of a telescope.

It could be extended or shortened like a telescope.

It is equal to the actual diameter of the cylinder of rays admitted by a telescope.

Newton's first telescope so far realized his expectations that he could see with its aid the satellites of Jupiter and the horns of Venus.

Her chief amusement during her leisure hours was sweeping the heavens with a small Newtonian telescope.

As the minimum focal length increases with the square of the aperture, a quite impracticable distance would be required to rival the resolving power of a modern telescope.

There appears to be no further advantage in the use of a telescope than the increased facility of accommodation, and for this of course a very low power suffices.

In observing the bands he received them at first upon a screen of finely ground glass, upon which a magnifying lens was focused; but it soon appeared that the ground glass could be dispensed with, the diffraction pattern being viewed in the same way as the image formed by the object-glass of a telescope is viewed through the eye-piece.

In addition to these open sights the bar also carries a sighting telescope.

The historical sequence of events now brings us to the discovery of the achromatic telescope.

My neighbor is interested in astronomy and bought a small telescope.

If you are using an achromatic refractor, the focus errors will be larger due to chromatic aberration of the telescope.

It would all depend on advances in computing and radio telescope technology.

In 1757 he presented a telescope to the king, so accurately driven by clockwork that it would follow a star all night long.

The only telescope erected in the establishment when he took it in charge was the transit instrument, and to this he vigorously devoted himself.

The spectra of the stars he obtained by using, outside the object-glass of his telescope, a large prism, through which the light passed to be brought to a focus in front of the eye-piece.

He arranges a selection from his observations on the nebulae in such a way as to give great plausibility to his view of the gradual transmutation of nebulae into stars Herschel begins by showing us that there are regions in the heavens where a faint diffused nebulosity is all that can be detected by the telescope.

The resolving power of a telescope with circular or rectangular aperture is easily investigated experimentally.

Merely to show the dependence of resolving power on aperture it is not necessary to use a telescope at all.

By varying the distance the point is easily found at which resolution ceases; and the observation is as sharp as with a telescope.

The (8), A function of the telescope is in fact to allow the use of a wider, and therefore more easily measurable, aperture.

The efficiency of a telescope is of course intimately connected with the size of the disk by which it represents a mathematical point.

The statement of the law of resolving power has been made in a form appropriate to the microscope, but it admits also of immediate application to the telescope.

If the origin of light be treated as infinitely small, and be seen in focus, whether with the naked eye or with the aid of a telescope, the whole of the light in the absence of obstacles would be concentrated in the immediate neighbourhood of the focus.

As an application of this result, let us investigate what amount of temperature disturbance in the tube of a telescope may be expected to impair definition.

P. Langley has proposed to obviate such ill-effects by stirring the air included within a telescope tube.

On the same principle we may estimate the least visible displacement of the eye-piece of a telescope focused upon a distant object, a question of interest in connexion with range-finders.

Let AoBo be a plane wave-surface of the light before it falls upon the prisms, AB the corresponding wave-surface for a particular part of the spectrum after the light has passed the prisms, or after it has passed the eye-piece of the observing telescope.

Observing through a telescope with light perpendicularly incident, he showed that the position of any ray was dependent only upon the grating interval, viz.

If, however, the half-covered aperture be in front of the object-glass, the phenomenon is magnified as a whole, and the desirable relation between the (unmagnified) dispersion and the aperture is the same as without the telescope.

It is true that the scale will require to be capable of being read with much greater accuracy than it th of an inch - for that, even in a telescope of 10 ft.

The limitation of power is introduced as in all optical instruments, by the finiteness of the length of a wave of light which causes the image of an indefinitely narrow slit to spread out over a finite width in the focal plane of the observing telescope.

He had equipped himself with a mental telescope and looked into remote space, where petty worldliness hiding itself in misty distance had seemed to him great and infinite merely because it was not clearly seen.

As the powers of the telescope were gradually developed, it was found that the finest hairs or filaments of silk, or the thinnest silver wires that could be drawn, were much too thick for the refined purposes of the astronomer, as p p they entirely obliterated the image of a star in the more powerful telescopes.

The great reflecting telescope at Dorpat was manufactured by him, and so great was the skill he attained in the making of lenses for achromatic telescopes that, in a letter to Sir David Brewster, he expressed his willingness to furnish an achromatic glass of 18 in.

One of these, of width equal, say, to one-tenth of an inch, is inserted in front of the object-glass, and the telescope, carefully focused all the while, is drawn gradually back from the grating until the lines are no longer seen.

If 2R be the diameter of the objectglass and D the distance of the object, the angle subtended by AP is E/D, and the angular resolving power is given by X/2 D sin a = X/2 R (3) This method of derivation (substantially due to Helmholtz) makes it obvious that there is no essential difference of principle between the two cases, although the results are conveniently stated in different forms. In the case of the telescope we have to deal with a linear measure of aperture and an angular limit of resolution, whereas in the case of the microscope the limit of resolution is linear, and it is expressed in terms of angular aperture.

Throughout the operation of increasing the focal length, the resolving power of the instrument, which depends only upon the aperture, remains unchanged; and we thus arrive at the rather startling conclusion that a telescope of any degree of resolving power might be constructed without an object-glass, if only there were no limit to the admissible focal length.

A rotation of this amount should therefore be easily visible, but the limits of resolving power are being approached; and the conclusion is independent of the focal length of the mirror, and of the employment of a telescope, provided of course that the reflected image is seen in focus, and that the full width of the mirror is utilized.

At a moment when the eye, or object-glass of a telescope, occupies a dark position, the star vanishes.

If a telescope be employed there is a distinction to be observed, according as the half-covered aperture is between the eye and the ocular, or in front of the object-glass.

In the former case the function of the telescope is simply to increase the dispersion, and the formation of the bands is of course independent of the particular manner in which the dispersion arises.

Fraunhofer; the latter ultimately attained considerable success and produced telescope disks up to 28 centimetres (II in.) diameter.

In 1848 Bontemps was obliged to leave France for political reasons and came to England, where he initiated the optical glass manufacture at Chance's glass works near Birmingham, and this firm ultimately attained a considerable reputation in the production of optical glass, especially of large disks for telescope objectives.

The price, however, rapidly increases with the total bulk of perfect glass required in one piece, so that large disks of glass suitable for telescope objectives of wide aperture, or blocks for large prisms, become exceedingly costly.

On the strength of similar arrangements of lenses and mirrors the invention of the camera obscura has also been claimed for Leonard Digges, the author of Pantometria (1571), who is said to have constructed a telescope from information given in a book of Bacon's experiments.

He was well acquainted with the use of magnifying glasses and suggested a kind of telescope for viewing the moon, but does not seem to have thought of applying a lens to the camera.

Wotton written to Lord Bacon in 1620 we learn that Kepler had made himself a portable dark tent fitted with a telescope lens and used for sketching landscapes.

In 1609 the telescope came into use, and the danger of observing the sun with it was soon discovered.

In 1611 Johann Fabricius published his observations of sun-spots and describes how he and his father fell back upon the old method of projecting the sun's image in a darkened room, finding that they could observe the spots just as well as with the telescope.

They do not seem to have used a lens, or thought of using the telescope for projecting an enlarged image on Kepler's principle.

It may be applied to the open end of a reflecting telescope, either of the Newtonian or the Cassegrain construction."

This was applied to an excellent achromatic telescope of 34 in.

There is also a position circle, attached at m to the eye-end, provided with a slide to move the eye-piece radially from the axis of the telescope, and with a micrometer to measure the distance of an object from that axis.

The chief objections to the method are that, as one star is in the axis of the telescope and the other displaced from it, the images are not both in focus of the eye-piece,3 and the rays from the two stars do not make the same angle with the optical axis of each segment.

On the other hand it is not necessary to reset the telescope after each reversal of the segments.4 When Bessel ordered the Konigsberg heliometer, he was anxious to have the segments made to move in cylindrical slides, of which the radius should be equal to the focal length of the object-glass.

Bessel's practice was to unclamp in declination, lower and read off the head, and then restore the telescope to its former declination reading, the clockwork meanwhile following the stars in right ascension.

The slowest speed is given by means of a tangent screw which is carried by a ball-bearing on the flange of the telescope sleeve, whilst its nut is double-jointed to a ring that encircles the flange of the heliometer-tube.

When the inclination of the movable half with respect to the axis of the telescope is changed by rotation about an axis at right angles to the plane of division, two images are produced.

The amount of separation is very small, and depends on the thickness of the glass, the index of refraction and the focal length of the telescope.

Helmholtz in his " Ophthalmometer " has employed Clausen's principle, but arranges the plates so that both move symmetrically in opposite directions with respect to the telescope axis.

Ramsden's dioptric micrometer consists of a divided lens placed in the conjugate focus of the innermost lens of the erecting eye-tube of a terrestrial telescope.

If Struve had employed a properly proportioned double circular diaphragm, fixed symmetrically with the axis of the telescope in front of the divided lens and turning with the micrometer, it is probable that his report on the instrument would have been still more favourable.

In the last the field is full of false light, and it is not possible to give sufficiently minute and steady separation to the images; and there are of necessity a collimator, two prisms of total reflection, and a small telescope through which the rays must pass; consequently there is great loss of light.

Such a prism he placed between the object-glass and eye-piece of a telescope.

By means of a cross-level the frame can be so adjusted that the cross axis on which the telescope is mounted is always truly horizontal.

This complication is eliminated in Scott's sight by simply levelling the cross axis of the telescope.

Personal error is to a great extent eliminated, power of vision extended, the sight is self-contained, there is no fore-sight, a fine pointer in the telescope being aligned on the target.

Disadvantages of earlier patterns were, the telescope was inverting, the drum was not graduated in yards, and drift not allowed for.

The advantages compared with a tangent sight are that only half the movement is required to raise the sight for any particular range; the ranges on the drum are easier to read, and if necessary can be set by another man, so that the layer need not take his eye from the telescope.

The pattern of telescope used in coast defence is that designed by Dr Common.

It has been in the past a source of much perplexity to observers of transits, but is now understood to be a result of irradiation, produced by the atmosphere or by the aberration of the telescope.

The fine castle of Birr, beside its historical interest, has gained celebrity on account of the reflecting telescope erected here (1828-1845) by William, third earl of Rosse.

In 1861 she removed from Nantucket to Lynn, where she used a large equatorial telescope presented to her by the women of America; and there she lived until 1865, when she became professor of astronomy and director of the observatory at Vassar College; in 1888 she became professor emeritus.

Before 1868 Maxwell conducted the experiment by sending light from the illuminated cross-wires of an observing telescope forward through the object-glass, and through a train of prisms, and then reflecting it back along the same path; any influence of convection would conspire in altering both refractions, but yet no displacement of the image depending on the earth's motion was detected.

For his Half-Hours with the Telescope (1868), which eventually reached a 10th edition, he received originally 25 from Messrs Hardwick.

From 1827 he devoted himself to the improvement of reflecting telescopes; in 1839 he mounted a telescope of 3 ft.

An inquirer who examines the stars with a shilling telescope is not likely to make observations of value, and even a trained astronomer has to allow for his "personal equation" - a point to which even a finished critic rarely attends.

When James Bradley and Samuel Molyneux entered this sphere of astronomical research in 1725, there consequently prevailed much uncertainty as to whether stellar parallaxes had been observed or not; and it was with the intention of definitely answering this question that these astronomers erected a large telescope at the house of the latter at Kew.

They determined to reinvestigate the motion of y Draconis; the telescope, constructed by George Graham (1675-1751), a celebrated instrument-maker, was affixed to a vertical chimneystack, in such manner as to permit a small oscillation of the eyepiece, the amount of which, i.e.

These results were unexpected, and, in fact, inexplicable by existing theories; and an examination of the telescope showed that the observed anomalies were not due to instrumental errors.

Many stars satisfy the condition of equality of polar distance with that of y Draconis, but few were bright enough to be observed in Molyneux's telescope.

The telescope serves to examine the image of the slit and to measure the angular separation of the different slit images; when photographic methods are employed the telescope is replaced by a camera.

The observing telescope is of the ordinary terrestrial form.

The scale telescope contains a graduated scale which is illuminated by a small burner; the scale is viewed by reflection from the prism face opposite the first refracting face.

Rutherfurd devised one made of flint glass with two crown glass compensating prisms; whilst Thallon employed a hollow prism containing carbon bisulphide also compensated by flint glass prisms. In direct vision spectroscopes the refracting prisms and slit are in the observing telescope.

By suitably replacing the ocular of the observing telescope in an angular vision spectroscope by a photographic camera, it is possible to photograph spectra; such instruments are termed spectrographs.

In grating spectroscopes both plane and concave gratings are employed in connexion with a collimator and observing telescope.

The position of the magnet is observed by means of a small telescope, and since the scale is at the principal focus of the lens, the scale will be in focus when the telescope is adjusted to observe a distant object.

Thus no alteration in the focus of the telescope is necessary whether we are observing the magnet, a distant fixed mark, or the sun.

The telescope B serves to observe the scale attached to the magnet when determining the magnetic meridian, and to observe the sun or star when determining the geographical meridian.

The magnet having been attached, the instrument is rotated about its vertical axis till the centre division of the scale appears to coincide with the vertical cross-wire of the telescope.

This mirror can rotate about a horizontal axis which is at right angles to the line of collimation of the telescope, and is parallel to the surface of the mirror.

The time of transit of the sun or star across the vertical wire of the telescope having been observed by means of a chronometer of which the error is known, it is possible to calculate the azimuth of the sun or star, if the latitude and longitude, of the place of observation are given.

If, however, a theodolite, fitted with a telescope which can rotate about a horizontal axis and having an altitude circle, is employed, so that when observing a transit the altitude of the sun or star can be read off, then the time need only be known to within a minute or so.

Hence in more recent patterns of magnetometer it is usual to do away with the transit mirror method of observing and either to use a separate theodolite to observe the azimuth of some distant object, which will then act as a fixed mark when making the declination observations, or to attach to the magnetometer an altitude telescope and circle for use when determining the geographical meridian.

The axis of the magnet is horizontal and at the same level as the mirror magnet, while when the central division of the scale B appears to coincide with the vertical cross-wire of the telescope the axes of the two magnets are at right angles.

In its simplest form it consists of a direct-vision spectroscope, having an adjustable slit (called "camera slit"), instead of an eyepiece, in the focal plane of the observing telescope.

This instrument, used since 1903 in conjunction with the Snow (horizontal) telescope of the Mount Wilson Solar Observatory, was constructed in the observatory instrument shop in Pasadena.

The upper plate PP is bored centrally to receive a parallel or conical pillar which supports the lower circle of the theodolite or the arm of the level which carries the telescope.

The verniers are attached to arms uu bearing on an enlargement of one trunnion of the telescope, one arm pro j ecting downwards and embracing a projection on the standard t.

The diagonal telescope nn is provided with cross hairs, and is used fcr the final centring of the instrument over an object.

The Y theodolite differs from the transit in that the supports for the telescope are low, that the telescope rests in a cradle the trunnions of which rest on the supports, and that a segment of a circle attached to the cradle replaces FIG.

When it is desired to read a line in the reverse direction the telescope is lifted out of the cradle, turned end for end, and replaced in the Y bearings of the cradle again.

In the Everest theodolite the supports are low and the telescope cannot be transited.

The eye end of the telescope tube is removed - a counterpoise to the object end being substituted in its place - and a prism is inserted at the intersection of the visual axis with the transit axis, so that the rays from the object-glass may be reflected through one of the tubes of the transit axis to an eye-piece in the pivot of this tube.

This is another surveying instrument consisting essentially of a telescope bearing a level and mounted horizontally upon a frame.

The upper plate is bored through the centre and carries a conical pillar, which rotates freely in it and supports a horizontal plate, to the extreme ends of which are attached, by means of capstan screws or otherwise, two vertical supports, on which the telescope, which is constructed to be perpendicular to the vertical axis of the instrument, rests and rotates with it.

The level bubble, by which the instrument is brought into a position at right angles to the axis of the earth, is generally placed on the top of the telescope.

The term "photographic telescope" has been applied to instruments employed to record the appearance of celestial objects by photography.

It was used by Galileo as early as 1612, and came into English use much later, when it supplanted trunk and cylinder, the terms hitherto used to denote the telescope.

Other passages from the Greek and Latin authors have similarly been cited to prove that the telescope was known to the ancients.

William Molyneux, in his Dioptrica Nova (1692), p. 256, declares his opinion that Roger Bacon (who died c. 12 9 4) "did perfectly well understand all kinds of optic glasses, and knew likewise the method of combining them so as to compose some such instrument as our telescope."

These passages certainly prove that Bacon had very nearly, if not perfectly, arrived at theoretical proof of the possibility of constructing a telescope and a microscope; but his writings give no account of the trial of an actual telescope, nor any detailed results of the application of a telescope to an examination of the heavens.

It has been pointed out by Dr Robert Smith, in his Complete System of Opticks, that Bacon imagines some effects of telescopes which cannot be performed by them, and his conclusion is that Bacon never actually looked through a telescope.

Wolfius infers from this passage that its author was the first actual constructor of a telescope, and it appears not improbable that by happy accident Porta really did make some primitive form of telescope which excited the wonder of his friends.

It is impossible to discredit the significance of these quotations, for the works in which they occur were published more than twenty years before the original date claimed for the discovery of the telescope in Holland.

But it is quite certain that previous to 1600 the telescope was unknown, except possibly to individuals who failed to see its practical importance, and who confined its use to "curious practices" or to demonstrations of "natural magic."

Jansen and his father were the real inventors of the telescope in 1610, and that Lippershey only made a telescope after hints accidentally communicated to him of the details of Jansen's invention.

They also prove that, whilst Metius was in possession of a telescope, with which he may have experimented, about the time when Lippershey presented his application for patent rights, yet.

The conclusion is that Lippershey was the first person who independently invented the telescope, and at the same time made the instrument known to the world.

He fitted the lenses in a tube, in order to adjust and preserve their relative distances, and thus constructed his first telescope.

The inverting telescope, composed of two, convex lenses, was a later invention; still it is not impossible that the original experiment was made with two convex lenses.

Sirturus, in his De Telescopio (1618), states that "a Frenchman proceeded to Milan in the month of May 1609 and offered a telescope for sale to Count di.

In his Saggiatore Galileo states that he solved the problem of the construction of a telescope the first night after his return to Padua from Venice, and made his first telescope next day by fitting a convex lens in one extremity of a.

Galileo may thus claim to have invented the telescope independently, but not till he had heard that others had done so.

Galileo devoted all his time to improving and perfecting the telescope.

His first telescope magnified three diameters; but he soon made instruments which magnified eight diameters, and finally one that magnified thirty-three diameters.'

Kepler first explained the theory and some of the practical advantages of a telescope constructed of two convex lenses in his Catoptrics (1611).

The first person who actually constructed a telescope of this form was the Jesuit Christoph Scheiner, who gives a description of it in his Rosa Ursina (1630).

William Gascoigne was the first who practically appreciated the chief advantages of the form of telescope suggested by Kepler, viz., the visibility of the image of a distant object simultaneously with that of a small material object placed in the common focus of the two lenses.

But it was not till about the middle of the 17th century that Kepler's telescope came into general use, and then, not so much because of the advantages pointed out by Gascoigne, but because its field of view was much larger than in the Galilean telescope.

The sharpness of image in Kepler's telescope is very inferior to that of the Galilean instrument, so that when a high magnifying power is required it becomes essential to increase the focal length.

Cassini discovered Saturn's fifth satellite (Rhea) in 1672 with a telescope of 35 ft., and the third and fourth satellites in 1684 with telescopes made by Campani of looand 136-ft.

James Bradley, on 27th December 1722, actually measured the diameter of Venus with a telescope whose objectglass had a focal length of 2124 ft.

In these very long telescopes This last power could not be exceeded with advantage in this form of telescope till after the invention of the achromatic objectglass.

He was well aware of the failures of all attempts to perfect telescopes by employing lenses of various forms of curvature, and accordingly proposed the form of reflecting telescope which bears his name.

But Gregory, according to his own confession, had no practical skill; he could find no optician capable of realizing his ideas, and after some fruitless attempts was obliged to abandon all hope of bringing his telescope into practical use.

Newton was the first to construct a reflecting telescope.

When in 1666 he made his discovery of the different refrangibility of light of different colours, he soon perceived that the faults of the refracting telescope were due much more to this cause than to the spherical figure of the lenses.

Encouraged by this success, he made a second telescope of 63-in.

A third form of reflecting telescope was devised in 1672 by Cassegrain (Journal des Scavans, 1672).

No further practical advance appears to have been made in the design or construction of the instrument till the year 1723, when John Hadley (best known as the inventor of the sextant) presented to the Royal Society a reflecting telescope of the Newtonian construction, with a metallic speculum of 6-in.

After remarking that Newton's telescope "had lain neglected these fifty years," they stated that Hadley had sufficiently shown "that this noble invention does not consist in bare theory."

Notwithstanding this difference in the brightness of the objects, we were able with this reflecting telescope to see whatever we have hitherto discovered with the Huygenian, particularly the transits of Jupiter's satellites and their shadows over his disk, the black list in Saturn's ring, and the edge of his shadow cast on his ring.

We have also seen with it several times the five satellites of Saturn, in viewing of which this telescope had the advantage of the Huygenian at the time when we compared them; for, being in summer, and the Huygenian telescope being managed without a tube, the twilight prevented us from seeing in this some of these small objects which at the same time we could discern with the reflecting telescope."

John Dollond, to whom the Copley medal of the Royal Society had been the first inventor of the achromatic telescope; but it was ruled by Lord Mansfield that" it was not the person who locked his invention in his scrutoire that ought to profit for such invention, but he who brought it forth for the benefit of mankind."3 In 1747 Leonhard Euler communicated to the Berlin Academy of Sciences a memoir in which he endeavoured to prove the possibility of correcting both the chromatic and.

We have thus followed somewhat minutely the history of the gradual process by which Dollond arrived independently at his invention of the refracting telescope, because it has been asserted that he borrowed the idea from others.

It is clearly established that Hall was the first inventor of the achromatic telescope; but Dollond did not borrow the invention from Hall without acknowledgment in the manner suggested by Lalande.

The limits of this article do not permit a further detailed historical statement of the various steps by which the powers of the telescope were developed.

The reflecting telescope became the only available tool of the astronomer when great light grasp was requisite, as the difficulty of procuring disks of glass (especially of flint glass) of suitable purity and homogeneity limited the dimensions of the achromatic telescope.

The former represents Kepler's, the latter Lippershey's or the Galilean telescope.

Also the diameter of the pencil or parallel rays emerging from the eye-lens to the diameter of the object-lens inversely as, the magnifying power of the telescope.

Hence one of the best methods of determining the magnifying power of a telescope to measure the diameter of the emergent pencil of rays, after the FIG.

The substitution of a positive or negative eye-piece for the simple convex or concave eye-lens, and of an achromatic object-glass for the simple object-lens, transforms these, early forms into the modern achromatic telescope.

For normal eyes the natural adaptation is not to focus for quiteparallel rays, but on objects at a moderate distance, and practically, therefore, most persons do adjust the focus of a telescope, for most distinct and easy vision, so that the rays emerge from the eye-piece very slightly divergent.

The magnifying power of the telescope is = Ff /ex, where F and f are respectively the focal lengths of the large and the small mirror, e the focal length of the eye-piece, and x the distance between the principal foci of the two mirrors (=Ff in the diagram) when the instrument is in adjustment for viewing distant objects.

Fewer telescopes have been made of this than perhaps of any other form of reflector; but in comparatively recent years the Cassegrain has acquired importance from the fact of its adoption for the great Melbourne telescope, and from its employment in the 60-in.

The magnifying power is computed by the same formula as in the case of the Gregorian telescope.

The Newtonian telescope is represented in Fig.

This form was adopted by the - elder Herschel to avoid the loss of light from reflection in the small mirror of the Newtonian telescope.

The front view telescope, however, has hardly been at all employed except by the Herschels.

The process of casting and annealing, in the case of the specula of the great Melbourne telescope, was admirably described by Dr Robinson in Phil.

Those silver-on-glass specula are now the rivals of the achromatic telescope, and it is not probable that many telescopes with metal specula will be made in the future.

Partly for these reasons the reflecting telescope with metallic mirror has never been a favourite with the professional astronomer, and has found little employment out of England.'

The proper mounting of a telescope is hardly of less importance than its optical perfection.

Where accurate differential observations or photographs involving other than instantaneous exposures have to be made, the additional condition is required that the optical axis of the telescope shall accurately and automatically follow the object under observation in spite of the apparent diurnal motion of the heavens, or in some cases even of the apparent motion of the object relative to neighbouring fixed stars.

Our limits forbid a historical account of the earlier endeavours to fulfil these ends by means of motions in altitude and azimuth, nor can we do more than refer to mountings such as those employed by the Herschels or those designed by Lord Rosse to overcome the engineering difficulties of mounting his huge telescope of 6 ft.

Both are abundantly illustrated in most popular works on astronomy, and it seems sufficient to refer the reader to the original descriptions.2 We pass, therefore, directly to the equatorial telescope, the instrument par excellence of the modern extra-meridian astronomer.

The article Transit Circle describes one form of mounting in which the telescope is simply a refined substitute for the sights or pinules of the old astronomers.

The present article contains a description of the mounting of the various forms of the so-called zenith telescope.

In its simplest form the mounting of an equatorial telescope consists of an axis parallel to the earth's axis, called" the polar axis "; a second axis at right angles to the polar axis called" the declination axis "; and the telescope tube fixed at right angles to the declination axis.

The telescope is counterpoised by a weight attached to the opposite end of the declination axis.

Thus, when the declination axis is horizontal the telescope moves in the plane of the meridian by rotation on the declination axis only.

Thus one important attribute of an equatorially mounted telescope that, if it is directed to any fixed star, it will follow the diurnal motion of that star from rising to setting by rotation of the polar axis only.

If we now attach to the polar axis a graduated circle D D, called the" hour circle,"of which the microscope or vernier R reads o h when the declination axis is horizontal, we can obviously read off the hour angle from the meridian of any star to which the telescope may be directed at the instant of observation.

Since the transit circle is preferable to the equatorial for such observations wherein great accuracy is required, the declination and hour circles of an equatorial are employed, not for the determination of the right ascensions and declinations of celestial objects, but for directing the telescope with ease and certainty to any object situated in an approximately known position, and which may or may not be visible to the naked eye, or to define approximately the position of an unknown object.

Further, by causing the hour circle, and with it the polar axis, to rotate by clockwork or some equivalent mechanical contrivance, at the same angular velocity as the earth on its axis, but in the opposite direction, the telescope will, apart from the effects of refraction, automatically follow a star from rising to setting.

The telescope is attached to one end of the declination axis, and counterpoised by a weight at the other end, as in fig.

The hour circle has two toothed circles cut upon it, one acted upon by a worm screw mounted on the pier and driven by clockwork, the other by a second worm screw attached to the polar axis, which can be turned by a handle in the observer's hand and thus a slow movement can be given to the telescope in right ascension inde FIG.

The other telescope is corrected for visual rays and its image is formed on the plane of the spider-lines of a filar micrometer.

Its success was such that the type of Fraunhofer's telescope became stereotyped for many years not only by Fraunhofer's successors but throughout Germany.

The driving circle is also much too small, so that a very slight mechanical freedom of the screw in the teeth involves a large angular freedom of the telescope in right ascension, while its position at the lower end of a too weak polar axis tends to create instability from torsion of that axis.

It is not a little curious that the obvious improvement of trans ferring the declination axis as well as the declination-clamp to the telescope end of the declination axis was so long delayed; we can explain the delay only by the desire to retain the declination circle as a part of the counterpoise.

The observer's eye is applied to the small telescope E, which (by means of prisms numbered I, 2, 3, 4) views the vernier attached to the cross-head simultaneously with the hour circle attached to the upper end of the polar axis.

Through the eyepiece of the bent 1 telescope E' another hour circle attached to the lower end of the polar axis can be seen; thus an assistant is able to direct the telescope by a handle at H to any desired hour angle.

A slight rotatory motion of the telescope E on its axis enables the vernier of the declination circle to be read through prism 1.

The mode of relieving the friction of the declination axis is similar to that employed in the Melbourne telescope and in the account of the Vienna telescope published by Grubb.

An excellent feature is the short distance between the eye-piece and the declination axis, so that 1 In the bent telescope refracting prisms are employed at the corners to change the direction of the rays.

This the Repsolds have done in the Pulkovo telescope by means of two platforms, as shown in fig.

These platforms are capable of easy motion so that the astronomer may be conveniently situated for observing an object at any azimuth or altitude to which the telescope may be directed.

This framework is provided with guides on which the platform, whilst preserving its horizontality, is V the observer has to follow the eye-end in a comparatively small circle; another good point is the flattening of the cast-iron centrepiece of the tube so that the flange of the declination axis is attached as near to the axis of the telescope tube as is consistent with free passage of the cone of rays from the object-glass.

The observer at the eye-end can also read off the hour and declination circles and communicate quick or slow motions, to the telescope both in right ascension and declination by conveniently Pulkovo, placed handles.

The largest refracting telescope in active use is the Yerkes telescope, with an object-glass of 40-in.

The telescope is moved in right ascension and declination by electric motors controlled from positions convenient for the observer.

The driving clock moves the telescope in right ascension by means of a worm-gear wheel, 10 ft.

For this purpose the telescope can be used in the four different ways shown in fig.

In Lassell's instrument (a reflector of the Newtonian type) the observer is mounted in the open air on a supplementary tower capable of motion in any azimuth about the centre of motion of the telescope, whilst an observing platform can be raised and lowered on the side of the tower.

Common's telescope presents many ingenious features, especially the relief-friction by flotation of the polar axis in mercury, and in the arrangements of the observatory for giving ready access to the eye-piece of the telescope.

In all these types the longer the telescope and the greater its diameter (or weight) the more massive must be the mounting and the greater the mechanical difficulties both in construction and management.

The difficulty is that the automatic motion of a single mirror capable of reflecting the rays of any star continuously along the axis of a fixed horizontal telescope, requires a rather complex mechanism owing to the variation of the angle of reflexion with the diurnal motion.

The largest refracting telescope yet made, viz., that constructed by Gautier for the Paris exhibition of 1900, was arranged on this plan (type F), the stars' rays being reflected along the horizontal axis re rac or of a telescope provided with visual and with photo graphic object-glasses of 49-in.

There are farther inconveniences in the use of such a telescope, viz., that the image undergoes a diurnal rotation about the axis of the horizontal telescope, so that, unless the sensitive plate is also rotated by clockwork, it is impossible to obtain sharp photographs with any but instantaneous exposures.

The mirrors of Lindemann's equatorial coude reflecting light downwards upon the mirror R would furnish an ideal siderostat for stellar spectroscopy in conjunction with a fixed horizontal telescope.

Thus, any fixed telescope directed towards the mirror of a properly adjusted coelostat in motion will show all the stars in the field of view at rest; or, by rotating the polar axis independently of the clockwork, the observer can pass in review all the stars visible above the horizon whose declinations come within the limits of his original field of view.

Therefore, to observe stars of a different declination it will be necessary either to shift the direction of the fixed telescope, keeping its axis still pointed to the coelostat mirror, or to employ a second mirror to reflect the rays from the coelostat mirror along the axis of a fixed telescope.

The Zenith Telescope The zenith telescope is an instrument generally employed to measure the difference between two nearly equal and opposite zenith distances.

The telescope is attached to one end of this axis and a counterpoise e to the other.

The long arm f serves to clamp the telescope in zenith distance and to communicate slow motion in zenith distance when so clamped.

On the side of the telescope opposite to the horizontal axis is attached a graduated circle g, and, turning concentrically with this circle, is a framework h, to which the readers and verniers of the circle are fixed.

The ob j ect-glass of the telescope is, of course, attached by its cell to the upper end of the telescope tube.

Within the focus of the object-glass is a right-angled prism of total reflection, which diverts the converging rays from the object-glass at right angles to the axis of the telescope, and permits the observing micrometer n to be mounted in the very convenient position shown in the figure.

This done, the stops s and t are clamped and adjusted so that when arm r comes in contact with the screw of stop t the telescope will point due north, and when in contact with s, it will point due south, or vice versa.

The telescope is now turned on the horizontal axis till the levels read near the centres of these scales and the telescope is clamped to the arm f.

If between the north and south observation there is a change in the level readings of the levels k and 1, this indicates a change in the zenith distance of the axis of the telescope.

On this principle the use of the level is abolished, the telescope is mounted on a metallic float, and it is assumed that, in course of the rotation of this float, the zenith distance of the axis of the telescope will remain undisturbed, that is, of course, after the undulations, induced by the disturbance of the mercury, have ceased.

The almucantar was therefore used only to observe the vertical transits of stars in different azimuths over fixed horizontal webs, without touching the telescope.

By the use of photography, however, it is possible to photograph the trail of a star as it transits the meridian when the telescope is directed towards the north, and another trail be similarly photographed when the telescope is directed towards the south.

When a telescope is employed this number is enormously increased, and still more so with the introduction of photographic methods; with modern appliances more than a hundred million of these objects may be rendered perceptible.

When examined with a telescope of power insufficient to separate the individual stars, a cluster appears like a nebula.

The brighter stars show a marked variety of colour in their light, and with the aid of a telescope a still greater diversity is noticeable.

If the uniform distribution extends indefinitely, or as far as the telescope can penetrate, the star-ratio should have the theoretical value 3.98, 1 any decrease in density or limit to the distribution of the stars will be indicated by a continual falling off in the star-ratio for the higher magnitudes.

Devoted to astronomy from his earliest years, he eagerly observed the heavens at a garret window with a telescope made by himself, and at nineteen began his career with the publication of a short work on the solar eclipse of the 5th of August 1766.

It is important for telescope objectives, since their apertures are so small as to permit higher orders to be neglected.

The Best Telescope Objectives, And Photographic Objectives Intended For Three Colour Work, Are Also Apochromatic, Even If They Do Not Possess Quite The Same Quality Of Correction As Microscope Objectives Do.

Galileo would not have wasted his time in corresponding with a man from whom he could learn nothing; and, though Sarpi did not, as has been asserted, invent the telescope, he immediately turned it to practical account by constructing a map of the moon.

At the meeting at which Newton was elected a description of a reflecting telescope which he had invented was read, and " it was ordered that a letter should be written by the secretary to Mr Newton to acquaint him of his election into the Society, and to thank him for the communication of his telescope, and to assure him that the Society would take care that all right should be done him with respect to this invention."

Then place a Lens of about three foot radius (suppose a broad Object-glass of a three foot Telescope), at the distance of about four or five foot from thence, through which all those colours may at once be transmitted, and made by its Refraction to convene at a further distance of about ten or twelve feet.

Among these subjects were the transit of Mercury, the Aurora Borealis, the figure of the earth, the observation of the fixed stars, the inequalities in terrestrial gravitation, the application of mathematics to the theory of the telescope, the limits of certainty in astronomical observations, the solid of greatest attraction, the cycloid, the logistic curve, the theory of comets, the tides, the law of continuity, the double refraction micrometer, various problems of spherical trigonometry, &c. In 1742 he was consulted, with other men of science, by the pope, Benedict XIV., as to the best means of securing the stability of the dome of St Peter's, Rome, in which a crack had been discovered.

This measurement is effected by a combination of two instruments, the telescope and the graduated circle.

These rays come to a focus at a point F lying in the focal plane of the telescope.

If the telescope is so pointed that the image of the star is seen in coincidence with the cross threads, as represented in fig.

If the telescope is moved around so that the images of two distant points are successively brought into coincidence with the cross threads, we know that the angle between the directions of D these points is equal to that through FIG.

This angle is measured by means of a graduated circle, rigidly attached to the tube of the telescope in a plane parallel to the line of sight.

When the telescope is turned in this plane, the angular motion of the line of sight is equal to that through which the circle has turned.

Its deviation from the vertical line is determined by the motion of the bubble of a spirit-level rigidly attached either to the axis, or to the telescope.

When the basin of quicksilver is used, the telescope, either before or after being directed toward P, is pointed directly downwards, so that the observer mounting above it looks through it into the reflecting surface.

The angular motion of the telescope in passing from this position to that when the celestial object is in the line of sight is the distance (ND) of the body from the nadir.

The telescope, in order that it may be pointed in any direction, must admit of two motions, one round the principal axis, and the other round an axis at right angles to it.

The unceasing diurnal motion of the image of any heavenly body relative to the cross threads of a telescope makes a direct accurate measure of any co-ordinate except the declination almost impossible.

The complexity of the problem will be seen by reflecting that the temperature of the air inside the telescope is not without its effect.

The descriptive branch found its principle of development in the growing powers of the telescope, and had little to do with mathematical theory; which, on the contrary, was closely allied, by relations of mutual helpfulness, with practical astronomy, or " astrometry."

Nevil Mas kelyne, who succeeded him in 1764, set on foot, in 1767, the publication of the Nautical Almanac, and about the same time had an achromatic telescope fitted to the Greenwich M aske mural quadrant.

The early observers seem to have been under the impression that the dark regions might be oceans; but this impression must have been corrected as soon as the telescope began to be improved, when the whole visible surface was found to be rough and mountainous.

He greatly improved both the telescope and microscope.

Even later, when the telescope was the only instrument of research, knowledge on this subject was confined to the appearances presented by the planets, supplemented by more or less probable inferences as to the nature of their surfaces.

Of polarimeters for the study of rotary polarization there are three principal forms. In Wild's polaristrobometer, light from a soda flame, rendered parallel by a lens, is polarized by a Nicol's prism, and after traversing the space into which the active substance is to be inserted, falls on a Savart's plate placed in front of an astronomical telescope of low power, that contains in its eyepiece a Nicol's prism, which with the plate forms a Savart's analyser.

A web in the focal plane of telescope marks the point in the field at which the bands are to be made to disappear; this is effected by turning the polarizer by means of a rack and pinion worked by an arm from the observer's end of the instrument.

The light is finally received in a Galilean telescope, containing an analyser and carried at the centre of a circular plate, that is graduated on its rim and can be turned in front of a vernier by means of a rack and pinion.

The telescope must be focussed on the edge of the quartz plate, and in order that all points of the field may be illuminated by the same part of the source, the flame must be so placed that its image is thrown by the lens on the diaphragm of the object glass of the telescope.

At one end of the instrument is placed a polarizer and the biquartz, and at the other a Galilean telescope, that must be focused on the edge of biquartz, having in front of its object-glass the compensator and an analyser that is regulated for producing the sensitive tint, when the plates of the compensator have the same thickness.

In order to correct this, the light after analysation is passed through another plate of quartz and then the sensitive tint may be more or less restored by cutting off some colour, the same for the whole field, by a Nicol's prism placed in the eyepiece of the telescope.

Galileo was not the original inventor of the telescope.

A rumour of the new invention, which reached Venice in June 1609, sufficed to set Galileo on the track; and after one night's profound meditation on the principles of refraction, he succeeded in producing a telescope of threefold magnifying power.

His researches with the telescope had been rewarded 1 The word telescope, from riiXe, far, to view, was invented by Demiscianus, an eminent Greek scholar, at the request of Prince Cesi, president of the Lyncean Academy.

In 1655 the word telescope was inserted and explained in Bagwell's Mysteries of Astronomy, trunk or cylinder being the terms until then ordinarily employed.

Such an instrument was made as early as 1590 by Zacharias Jansen of Middleburg; and although Galileo discovered, in 1610, a means of adapting his telescope to the examination of minute objects, he did not become acquainted with the compound microscope until 1624 when he saw one of Drebbel's instruments in Rome, and, with characteristic ingenuity, immediately introduced some material improvements into its construction.

Convex glass lenses were first generally used to assist ordinary vision as " spectacles "; and not only were spectacle-makers the first to produce glass magnifiers (or simple microscopes), but by them also the telescope and the compound microscope were first invented.

The arrangement of two lenses so that small objects can be seen magnified followed soon after the discovery of the telescope.

The first compound miscroscope (discovered probably by the Middelburg lens-grinders, Johann and Zacharias Janssen about 1590) was a combination of a strong biconvex with a still stronger biconcave lens; it had thus, as well as the first telescope, a negative eyepiece.

Selligue had no particular comprehension of the problem, for his achromatic single systems were simply telescope objectives corrected for an infinitely distant point, and were placed so that the same surface was turned towards the object in the microscope objective as in the telescope objective; although contrary to the telescope, the distance of the object in the microscope objective is small in proportion to the distance of the image.

The first binocular telescope, consisting of two telescopes placed side by side, was.

This instrument shows a transition to the stereoscope, inasmuch as the scale or means of measurement is not directly observed, but to each eye a plane representation is offered, just as in the stereoscope; the space to be measured, on the other hand, is portrayed in exactly the same way as in the double telescope.

The problem is that the range distance to the sodium beacon constantly changes with weather and telescope zenith angle.

The doctor will use a small telescope (called an arthroscope) to look inside your knee.

Within a few years of Tycho's death, the telescope had revolutionized observational astronomy.

An optical telescope is used with a special detector called a bolometer placed at its focus.

The classical Cassegrain In the classical Cassegrain telescope, the primary mirror is paraboloid shaped.

Cassegrain telescope feeds is in progress.

I cannot show some images directly from my scope unfortunately because I don't own the 30mm diameter Zeiss phase telescope.

These include intussusception, when the adenoma may act as a lead point and cause the duodenum to telescope on itself.

No degradation of telescope IR emissivity, which is a crucial advantage for a system with strong science drivers in the infrared.

The aluminum tube has an outside diameter of 1 1/4 inches to suit standard telescope eyepiece sizes.

There is even a telescope available for members to hire at a nominal fee.

In my own case I once ran upon a situation in which the telescope sight was a positive hindrance.

The surgeon uses a type of telescope, called a laparoscope, to do the operation.

The military genius A 19 th century lithograph, showing Napoleon peering through a telescope.

Once you have these figures you also need to discover the maximum magnification the telescope is capable of.

The telescope was completed on 28th August 1789 and on that first night, Herschel discovered two new moons of Saturn.

The calibration unit produces a beam that matches the telescope pupil very nicely except that it contains no central obscuration.

Registration is performed using the telescope offsets transformed to pixels.

To help you to choose a telescope or binoculars, or to understand telescope optics visit my Choosing a Telescope page.

In these exposures the atmospheric phase perturbations are compensating for the errors in the figure of the telescope mirror.

This is an ideal telescope for high power planetary viewing as well as imaging.

Eventually, in 1965, Penzias and Wilson had a radio telescope.

The means by which the Group plans to undertake its study is a new 2.6 meter diameter radio telescope.

The WSRT was the first radio telescope to detect and map the spiral arms of another galaxy, M 51.

Doubtless you know that Swarovski can now provide you with a telescope sight for your rifle which includes a built-in laser range finder.

It is NOT possible for the telescope to have the Cassegrain rotator fixed and for you to simultaneously specify the field orientation.

There are two sorts of rifle which I think are better off without telescope sights.

Through his telescope Galileo saw craters on the Moon and observed sunspots.

A 100mm diameter, 500mm focal length refracting telescope was used, equipped with a solar filter.

This makes for a fast and very easy method for aligning the telescope.

In 1672 Newton made contact with the Royal Society, presenting his design for a reflecting telescope.

For example, in 2001, UK astronomers, using the Anglo-Australian telescope, discovered three planets orbiting another star.

Students will be given a chance to use brand new astronomical telescope over the internet.

Among the exhibits is a 28 inch refractor telescope, one of the largest in the world.

The fluxgate sensor mounted on the telescope of a non-magnetic theodolite is used to detect when it is perpendicular to the magnetic field vector.

The great telescope was suspended on a gigantic frame and could be seen towering above the Slough town center.

Now that telescope sights are practically universal on sporting rifles, the proper design of iron sights has become an abandoned topic.

But mirror sizes up to 16 inches are often used - but then the telescope become heavy and somewhat unwieldy.

Here are the planets and some of their moons, all visible with a good telescope, some visible with a good telescope, some visible with the naked eye.

Residual jitter can arises from uncorrected atmospheric turbulence as well as telescope wind shake.

Before the invention of the telescope the accuracy of astronomical observations was necessarily limited by the angle that could be distinguished by the naked eye.

The principle of Gascoigne's micrometer is that two pointers having parallel edges at right angles to the measuring screw, are moved in opposite directions symmetrically with and at right angles to the axis of the telescope.

This screw is mounted on an oblong box which carries one of the measuring edges; the other edge is moved by the coarser part of the screw relatively to the edge attached to the box, whilst the box itself is moved relatively to the axis of the telescope by the finer screw.

Upon an axis concentric with the declination axis is carried a plane mirror, which is geared so as always to bisect the angle between the polar axis and the optical axis of the telescope.

When the instrument has been set up and levelled (either with aid of the cross level d, or the levels k and 1), the reading of the circle p for the meridional position of the telescope is determined either by the method of transits in the meridian (see Transit Circle), or by the observation of the azimuth of a known star at a known hour angle.

By directing the telescope to a distant object, or to the intersection of the webs of a fixed collimating telescope (see Transit Circle), it is easy to measure the effect of a small change of zenith distance of the axis of the telescope in terms both of the level and of the micrometer screw, and thus, if the levels are perfectly sensitive and uniform in curvature and graduation, to determine the value of one division of each level in terms of the micrometer screw.