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micrometer

micrometer

micrometer Sentence Examples

  • MICROMETER (from Gr.

  • It became, in fact, essential to invent a " micrometer " for measuring the small angles which were thus for the first time rendered sensible.

  • inventor of the micrometer.

  • The micrometer so mentioned fell into the possession of Richard Townley of Lancashire, who exhibited it at the meeting of the Royal Society held on the 25th of July 1667.

  • The micrometer is at zero when the two edges are brought exactly together.

  • A steel cylinder (about the thickness of a goose-quill), which forms the micrometer screw, has two threads cut upon it, one-half being cut with a thread double the pitch of the other.

  • (1773), p. 190) also gives results of measurements by Gascoigne of the diameters of the moon, Jupiter, Mars and Venus with his micrometer.

  • Huygens, in his Systema saturnium (1659), describes a micrometer with which he determined the apparent diameters of the principal planets.

  • The Marquis Malvasia in his Ephemerides (Bologna, 1662) describes a micrometer of his own invention.

  • The micrometer of Auzout and Picard was provided with silk fibres or silver wires instead of the edges of Gascoigne, but one of the silk fibres remained fixed while the other was moved by a screw.

  • Beyond the introduction of the spider line it is unnecessary to mention the various steps by which the Gascoigne micrometer assumed the modern forms now in use, or to describe in detail the suggestions of Hooke, 4 Wren, Smeaton, Cassini, Bradley, Maskelyne, Herschel, Arago, Pearson, Bessel, Struve, Dawes, &c., or the successive productions of the great artists Ramsden, Troughton, Fraunhofer, Ertel, Simms, Cooke, Grubb, Clarke and Repsold.

  • The Modern Filar Micrometer.

  • When equatorial mountings for telescopes became more general, no filar micrometer was considered complete which was not fitted with a position circle.'

  • The use of the spider line or filar micrometer 1 In 1782 (Phil.

  • A still further facility was given to the use of the filar micrometer by the introduction of clockwork, which caused the telescope automatically to follow the diurnal motion of a star, and left the observer's hands entirely at liberty.'

  • The micrometer represented in figs.

  • They are placed at a distance apart less than the focal length of a, so that the wires of the micrometer, which must be distinctly seen, are beyond b.

  • The eyepiece slides into the tube cd, which screws into the brass ring ef, through two openings in which the oblong frame, containing the micrometer slides, passes.

  • The slides are accurately fitted so as to have no sensible lateral shake, but yet so as to move easily in the direction of the greatest length of the micrometer box.

  • One of the most essential points in a good micrometer is that all the webs shall be so nearly in the same plane as to be well in focus together under the highest powers used, and at the same time absolutely free from " fiddling."

  • the micrometer by Trough ton, fitted to their 5 ft.

  • equatorial telescope, is the first position micrometer constructed capable of measuring position angles to 1' of arc.

  • The English micrometer still retains the essential features of Troughton's original construction above described.

  • The later English artists have somewhat changed the mode of communicating motion to the slides, by attaching the screws pdrmanently to the micrometer head and tapping each micrometer screw into its slide.

  • The micrometer represented in fig.

  • 5 is the original Merz micrometer of the Cape Observatory, made FIG.

  • S is the head of the micrometer screw proper, s that of the screw moving the slide to which the so-called " fixed web " is attached, s' that of a screw which moves the eyepiece E.

  • In this micrometer the three slides moved by S, s, and s' are simple dovetails.

  • For the internal structural details of the micrometer the reader is referred to the article " Micrometer " in the 9th edition of the Encyclopaedia Britannica.

  • To measure distances with the Fraunhofer micrometer, the position-circle is clamped at the true position-angle of the star, and the telescope is moved by its slow motions so that the component A of the star is bisected by the fixed wire; the other component B is then bisected by the web, which is moved by the graduated head S.

  • Dawes, who employed a micrometer of the English type (figs.

  • I, 2 and 3), used to bolt the head of one of the screws, and the instrument was provided with a slipping piece, giving motion to the micrometer by screws acting on two slides, one in right ascension, the other in declination, so that " either of the, webs can be placed upon either component of a double star with ease and certainty (Mem.

  • The micrometer shown in fig.

  • micrometer with the upper side of the box removed.

  • The latter are in fact little microscopes carrying a vernier etched on glass, in lieu of a filar micrometer.

  • With the Cape micrometer a systematic difference has been found in the coincidence point for head above and head below amounting to o"-14.

  • The short screw whose divided milled head is shifts the zero of the micrometer by pushing, without turning, the short sliding rod whose flat end forms the point d'appui of the micrometer screw at I.

  • a convenient feature in Repsolds' micrometer that the webs are very near the inner surface of the top of the box, so that the eye is not brought inconveniently close to the plate when high powers are used.

  • Da and The micrometer box, and of course with it the whole system of spider webs, is moved by the screw s, whilst the measuring web is independently moved by the screw S.

  • The method of counting the total number of revolutions gives more friction and is less convenient than Repsolds', and no provision seems to be made for illuminating the micrometer head in the practical and convenient plan adopted by Repsolds.

  • Repsolds' more recent form of the spider-line micrometer (since 1 The marks of varnish so applied will he seen in fig.

  • The micrometer is clamped in FIG.

  • The end-plane of this cylinder receives the pressure of the micrometer screw, so that by turning the small drum-head the coincidence-reading of the movable web with the fixed web can be changed, and thus any given angle can be measured with different FIG.

  • The electric lamp a gives illumination of the webs in a dark field, nearly in the manner described for the Cape transit circle micrometer; the intensity of illumination is regulated by a carbon-resistance controlled by the screw b.

  • The illumination of the field is given by a lamp near the object glass, controlled by a switch near the micrometer.

  • The same firm is also constructing a micrometer in which the readings of the head are printed on a band of paper instead of being read off at the time of observation.

  • Instruments have been invented by Alvan Clark and Sir Howard Grubb for measuring with the spider-line micrometer angles which are larger than the field of view of the eyepiece.

  • Grubb's duplex micrometer is described in the 9th edition of the Encyclopaedia Britannica.

  • We have not had an opportunity of testing this, nor Grubb's more recent models; but, should it be found possible to produce such images satisfactorily, without distortion and with an apparatus convenient and rigid in form, such micrometers may possibly supersede the filar micrometer.

  • reseau-square by means of a spider-line micrometer, a glass scale, on the plan shown in fig.

  • This involves a loss of accuracy because, with a spiderline micrometer, the accidental error of pointing is of the order of o I" of arc.

  • In the measuring machines in general use the field of view, as in the case of the glass-scale micrometer, is sufficiently large to include the image of the 5 mm.

  • The microscope or viewing telescope is fitted with a spider-line micrometer having two screws at right angles to each other, by means of which readings can be made first on one reseau-line, then on the star, and finally on the opposite reseau-line in both co-ordinates.

  • This form of micrometer is of course capable of giving results of high precision, but the drawback is that the process involves a minimum of six pointings and the entering of six screw-head readings in order to measure the two co-ordinates of the star.

  • The object glass of the micrometer-microscope is placed midway between the plane of the photographic plate and the plane of the micrometer webs.

  • The micrometer is provided with a " fixed square " 5 mm.

  • - Diagram of the diaphragm in eyepieces of " the micrometer used for measuring the plates of the Astrographic Catalogue.

  • Two other screws, o, p, the heads of which are not graduated, give motions to the whole micrometer box through t 1 mm.

  • All the essential parts of the micrometer, including the slides, micrometer box, tube, etc., are of steel or cast-iron, so that changes of temperature do not affect the adjustments.

  • The micrometer readings for coincidence of the movable webs with the webs of the fixed square shall be exactly 0 000R and io-000R.

  • By means of the quick rack motions A and B move the plate so as to bring the reseau-square into the centre of the field of the micrometer; then, by means of the screw heads o, p, perfect the coincidence of the " fixed square " of webs, with the image of the reseau-square.

  • Its fundamental principle is that, by a combination of glass scales with a micrometer screw, " the chief part of the distance to be measured is read off on the scale; the fractional part of the scalespace is not estimated but measured by the screw."

  • An important modern application of the micrometer, which is not dealt with in the article Transit Circle, is that which is now called " the travelling wire micrometer."

  • 2940, Dr Repsold proposed a method of meridian observing which consists in causing a web to follow the image of a star in transit by motions communicated by the observer's hands alone, whilst electrical contacts on the drum of the micrometer screw register on the chronograph the instants corresponding to known intervals from the line of collimation.

  • 3377, Repsold gives a detailed description of two forms of eye-ends of transit circles, fitted with means of observing in this manner, to which he gives the name of " the impersonal micrometer."

  • It should be mentioned that an essential feature of the travelling wire micrometer is that the eyepiece as well as the wire shall be moved by the micrometer-screw.

  • The method originally used by Huggins, who first conceived and proved the possibility of measuring stellar velocities in the line of sight, was to measure with a filar micrometer the displacement of some well-known line in a stellar spectrum relative to the corresponding line of a terrestrial spectrum.

  • The capillary tube can be raised or lowered at will by running a magnet outside the tube, and the heights of the columns are measured by a cathetometer or micrometer microscope.

  • The position of the middle of the bright band representative of a mathematical line can be fixed with a spider-line micrometer within a small fraction of the width of the band, just as the accuracy of astronomical observations far transcends the separating power of the instrument.

  • The present article also deals with other forms of double-image micrometer.

  • It would appear that to Servington Savary is due the first invention of a micrometer for measurement by double image.

  • The small interval between the adjacent limbs was then measured with a wire micrometer.

  • p. 551) in which he shows that a micrometer can be much more easily constructed by dividing a single object-glass through its axis than by the employment of two object-glasses.

  • be used as a micrometer: " I.

  • Considering the accuracy of these measures (an accuracy far surpassing that of any other contemporary observations), it is somewhat surprising that this form of micrometer was never systematically used in any sustained or important astronomical researches, although a number of instruments of the kind were made by Dollond.

  • This construction would give all the advantage of the younger Dollond's object-glass micrometer, and more than its sharpness of definition, without liability to the systematic errors which may be due to want of homogeneity of the object-glass; for the lenses will not be turned with respect to each other, but, in measurement, will always have the same relation in position angle to the line joining the objects under observation.

  • focus, would correspond with 2" of arc. But, after all, this is no practical difficulty, for screws can be used to separate the lenses, and, by these screws, as in a Gascoigne micrometer, the separation of the lenses can be measured; or we can have scales for this purpose, read by microscopes, like the Troughton 1 circles of Piazzi or Pond, or those of the Carey circle, with almost any required accuracy.

  • To Bouguer in 1748 is due the true conception of measurement by double image without the auxiliary aid of a filar micrometer, viz.

  • 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.

  • This ring is necessary in order to allow the rods to follow the micrometer heads when the position angle is changed.

  • For this purpose the position angle of the eye-piece micrometer is set to that of the head, and the eye-piece is displaced from the axis of the tube (in the direction of the movable segment) by an amount equal to half the angle under measurement.

  • 4) that Bessel had indicated, by notes in his handbooks, the following points which should be kept in mind in the construction of future heliometers: (I) The segments should move in cylindrical slides; b (2) the screw should be protected from dust; 6 (3) the zero of the position circle should not be so liable to change; 7 (4) the distance of the optical centres of the segments should not change in different position angles or otherwise; 8 (5) the points of the micrometer screws should rest on ivory plates; 9 (6) there should be an apparatus for changing the screen.'° Wilhelm Struve, in describing the Pulkowa heliometer,' 1 made The distances of the optical centres of the segments from the eye-piece are in this method as I; secant of the angle under measurement.

  • 2 Steinheil applied such motion to a double-image micrometer made for Struve.

  • means of measuring the focal point were provided; symmetrical motion was given to the slides; scales on each slide were provided instead of screws for measuring the separation of the segments, and both scales were read by the same micrometer microscope; a metallic thermometer was added to determine the temperature of the scales.

  • a is the eye-piece fixed in the optical axis, b the micrometer for reading both scales.

  • to), for the purpose of interposing at pleasure the prism it in the axis of the reading micrometer; this enables the observer to view the graduations on the face of the metallic thermometer TT (composed of a rod of brass and a rod of zinc).

  • a is the eye-piece, b the handle for moving the segments, c the micrometer microscope for reading the scales and scale micrometer, d the micrometer readers of the position and declination circles, e the handle for rotating the large wheel E which carries the screens.

  • Elkin found that the chief drawbacks to speed and convenience in working this heliometer were: (I) The loss of time involved in entering the corresponding readings of the micrometer pointings on two scales.

  • To remedy drawback (I) Repsolds devised the form of printing micrometer which is shown in figs.

  • This micrometer is provided with two pairs of parallel webs.

  • 54 shows the record of several successive paintings on the same scale as that given by the micrometer.

  • and Dec. of the object to be observed, the scale divisions to be pointed upon, and thus, in measures of distance, with the aid of the chronograph and printing micrometer, enable the observer to adjust the instrument for observation and obtain a record of his observations without the aid of a hand-lamp or the necessity to make any records in his notebook.

  • Having selected the most suitable one he directs the axis of the finder to the estimated middle point between the comet and the star, turns the finder-micrometer in position angle until the images of comet and star lie symmetrically between the parallel position wires, and then turns the micrometer screw (which moves the distance-wires symmetrically from the centre in opposite directions) till one wire bisects the comet and the other the star.

  • 414) proposed a form of micrometer consisting of a divided plate of parallel glass placed within the cone of rays from the object-glass at right angles to the telescope axis.

  • Angelo Secchi (Comptes rendus, xli., 18 55, p. 906) gives an account of some experiments with a similar micrometer; and Ignarjio Porro (Comptes rendus, xli.

  • p. 1058) claims the original invention and construction of such a micrometer in 1842.

  • Should Clausen's micrometer be employed as an astronomical instrument, it would be well to adopt the improvement of Helmholtz.

  • 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.

  • xvii., 1815, pp - 344-359) describes a micrometer in which a negative lens is introduced between the eye-piece and the objectglass.

  • In the improved form' of Airy's divided eye-glass micrometer (Mem.

  • pp. 199-209) the rays from the object-glass pass successively through lenses as follows: The lens b is divided, and one of the segments is moved by a micrometer screw.

  • There is only one practical published investigation of Airy's micrometer that is worthy of mention, viz.

  • Dawes successfully employed the double circular aperture also with Amici's micrometer.

  • It is essentially the same in principle as Amici's micrometer, except that the divided lens is an achromatic positive instead of a negative lens.

  • He, however, successfully employed the instrument in measuring double stars, so close as I" or 2", and using a power of 300 diameters, with results that agreed satisfactorily amongst themselves and with those obtained with the filar micrometer.

  • 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.

  • Arago made many measures of the diameters of the planets with such a micrometer.

  • Trans., 1821, pp. 101-103) describes a doubleimage micrometer of his own invention, in which a sphere of rockcrystal is substituted for the eye-lens of an ordinary eye-piece.

  • Yet the beautiful images which these micrometers give permit the measurement of very difficult objects as a check on measures with the parallel-wire micrometer.

  • A micrometer drum reads to 2', while the vernier reads to single minutes so that very fine adjustments can be made.

  • In Scott's sight, mark iv., there is a longitudinal level pivoted at one end and provided with a degree scale up to 4°; the level is moved by a spindle and micrometer screw reading to 2'.

  • If now the telescope be directed on the target and this level be brought to the centre of its run, the angle of sight can be read - if afterwards any range ordered is put on the sight and the gun truly layed, this bubble will be found in the centre of its run - so that if thereafter the target becomes obscured the gun can be relayed by elevating till the bubble is in the centre of its run, or at a completely concealed target the angle of sight can, if the range and difference of level are known or can be measured from somewhere near the gun, be put on by means of the micrometer screw, and the gun subsequently layed by putting the range in yards or degrees on the sight drum and elevating or depressing till the bubble is central.

  • The collimator has a vertical slit at its outer end, the width of which may be regulated by a micrometer screw; in some instruments one half of the slit is covered by a small total reflection prism which permits the examination of two spectra simultaneously.

  • The slit is narrowed down to the desired width, and moved as a whole by a micrometer screw, until it coincides with the cross-hair.

  • Every time, therefore, that a speculum is repolished, the future quality of the instrument is at stake; its focal length will probably be altered, and thus the value of the constants of the micrometer also have to be redetermined.

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

  • The peculiar form of the tube is eminently suited for rigid preservation of the relative parallelism of the axes of the two telescopes, so that,;i the image of a certain selected star is retained on the intersection of two wires of the micrometer, by means of the driving clock, aided by small corrections given by the observer in right ascension and declination (required on account of irregularity in the clock movement, error in astronomical adjustment of the polar axis, or changes in the star's apparent place produced by refraction), the image of a star will continue on the same spot of the photographic film during the whole time of exposure.

  • The eye-end carries the micrometer with an illuminating apparatus similar to that described under Micrometer.

  • The lamp near the eye-end illuminates the field or the wires at pleasure, as well as the position circle of the micrometer and the declination circle; a separate lamp illuminates the hour circle.

  • The eye end presents an refractor appearance too complicated to be figured here; it has a micrometer and its illumination for the position circle, a micrometer head, and a bright or dark field, clamps in right ascension and declination and quick and slow motion in the same, a finder, microscopes for reading the hour and declination circles, an illuminated dial showing sidereal time and driven by an electric current from the sidereal clock, and counter weights which can be removed when a spectroscope or other heavy appliance is added.

  • 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.

  • When the star enters the field of view its image is approximately bisected by the spider web of the micrometer n, the exact bisection being completed in the immediate neighbourhood of the meridian.

  • Suppose now, for the moment, that the readings of the levels k and l are identical in both observations, we have then, in the difference between the micrometer readings north and south, a measure of the difference of the two zenith distances expressed in terms of the micrometer screw; and, if the "` value of one revolution of the micrometer screw" is known in seconds of arc we have for the resulting latitude FIG.

  • - Zenith Telescope (by Warner & SwaseY) 4 - 2{(n -)+(Sn+ss)I, where - t 5 is the difference of the micrometer readings converted into arc - it being assumed that increased micrometer readings correspond with increased zenith distance of the star.

  • The value of "one revolution of the screw in seconds of arc" can be determined either by observing at transit the difference of zenith distance of two stars of known declination in terms of the micrometer screw, the instrument remaining at rest between their transits; or by measuring at known instants in terms of the screw, the change of zenith distance of a standard star of small polar distance near the time of its greatest elongation.

  • It is, however, obviously impossible to apply a micrometer with advantage to such instruments, because to touch such an instrument, in order to turn a micrometer screw, would obviously set it into motion.

  • divisions of the micrometer scale in the eye-piece of the microscope, 54 divisions being equal to one millimetre.

  • This in its simplest form consisted of a ring of wire nearly closed terminating in spark balls very close together, adjustable as to distance by a micrometer screw.

  • He found that when the resonator was placed in certain positions with regard to the oscillator, small sparks were seen between the micrometer balls, and when the oscillator was placed at one end of a room having a sheet of zinc fixed against the wall at the other end, symmetrical positions could be found in the room at which, when the resonator was there placed, either no sparks or else very bright sparks occurred at the poles.

  • 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.

  • Among them were an elegant solution of the problem to determine the orbit of a comet from three observations, and memoirs on the micrometer and achromatic telescopes.

  • William Gascoigne's invention of the filar micrometer and of the adaptation of telescopes to graduated instruments remained submerged for a quarter of a century in consequence of his untimely death at Marston Moor (1644).

  • The most used is the micrometer screw adjustment (fig, 51).

  • - Micrometer Screw FIG.

  • The end of the column C is traversed by the micrometer screw D which is set in action by the knob E.

  • By screwing in the micrometer, the spring is compressed and the tube lowered.

  • In other fine adjustments by means of springs and balance wheels either a micrometer screw is moved (Zeiss), or a curved disk fixed to the balance wheel is turned (Leitz), or an oblique disk arranged more or less in a circle and attached to the balance wheel is revolved (Reichert).

  • The first method uses the objective screw micrometer.

  • The object is placed on a slide in the plane of the stage plate and able to be very finely moved by the micrometer screw, which has as fine a worm as possible.

  • After the microscope has been so adjusted that the image of the object to be measured falls exactly in the plane of the cross threads, the object is moved by the micrometer until one edge of the object is exactly covered by a thread.

  • The micrometer is now read.

  • Then the object is moved by the micrometer till the image of the other edge is covered by the thread in the eyepiece, and the micrometer is again read.

  • The objective screw micrometer is, however, not sufficiently delicate, and is only used when comparatively large objects are to be measured, and especially for objects whose edges do not appear at the same time in the field of view.

  • The second and most widely used method employs a micrometer eyepiece.

  • - Screw Micrometer Ocular.

  • eyepiece a slide b can be moved by a micrometer screw a; the slide carries a little glass plate c provided with a graduation.

  • The micrometer stands at zero if the zero mark of the cylinder coincides with the index and the fixed mark is at a known division.

  • The calculation is most convenient if the micrometer is left in the position of zero and the object is moved till one of its edges corresponds to the zero mark of the eyepiece scale.

  • If the micrometer is then moved till another graduation corresponds to the other edge of the image the size of the image can be read off.

  • by using an objective micrometer.

  • A fine scale with known intervals is put on the stage plate, and by determining the distance between the graduations of the objective micrometer formed through the same objective, by means of the screw micrometer ocular, the magnification of the objective is determined.

  • As the errors in the graduation of the objective micrometer are also magnified, very exact scales are necessary.

  • A fixed eyepiece micrometer is simpler and more popular.

  • By using an objective micrometer in place of the object, the magnification of the objective can be ascertained and from this the actual size of the object.

  • As fractions of intervals can only be estimated in this method, a measurement with such an eyepiece scale can of course not be as exact as with a screw micrometer ocular.

  • If, as before, an objective micrometer is placed below the microscope in the place of the object, and the size of a special micrometer-interval is drawn on the same board, then the actual size of the object can be ascertained.

  • Instead of first drawing the object and the objective micrometer, they can of course be projected at the same moment on a scale on the drawing board.

  • The errors attending the determination of the size of a microscopic object depend chiefly on the accuracy of the objective micrometer; any errors in the micrometer being magnified by the objective.

  • These may be diminished by using different parts of the objective micrometer for the correction of the eyepiece scale, and the calculation of the size is based on the found mean value.

  • A second error can arise through the inaccuracy of the eyepiece micrometer, and also in the case of a screw micrometer through periodic faults of the screw, and through dead motion.

  • The eyepiece micrometer allows its errors to be diminished, if one measures at different points and then fixes a mean value.

  • The dead motion of a micrometer screw is best avoided by working the screw always from one and the same side.

  • If the object can be seen by using the mirror, the plane mirror must be used; then the actual size of the object and of the image produced by the objective is measured (of the image by a micrometer ocular).

  • The focal length of an objective can be more simply determined by placing an objective micrometer on the stage and reproducing on a screen some yards away by the objective which is to be examined.

  • If the size of the image of a known interval of the objective micrometer is determined by an ordinary scale, and the distance of the image from the focal plane of the objective belonging to it is measured, then the focal length can be calculated from the ratio y/y'=fl', in which y is the size of the object, y' that of the image, and xi' the distance of the image from the focal plane belonging to it.

  • If a drawing prism is used above the eyepiece, and an objective micrometer is inserted, then if a scale is laid on the drawing board which is 25 cm.

  • distant from the exit pupil, one or more intervals of the objective micrometer can be seen projected on the scale lying on the board.

  • aliquot of the sample was filtered through a 0.45 micrometer membrane filter into an autosampler vial ready for analysis.

  • To modern eyes the unit does lack something in the way of bulk and the micrometer dials were obviously far too small.

  • eyepiece micrometer.

  • filar micrometer eyepiece allows me to make accurate measurement of cell dimensions.

  • Details of past projects of the CMT using the old micrometer can be found here.

  • This difference in extrudate swell magnitude was also observed in results obtained using the laser scanning micrometer.

  • To calibrate the eyepiece micrometer, the stage micrometer has to be focused using the objective to be used.

  • These differences were observed in results obtained using both the laser scanning micrometer and the hand-held micrometer.

  • Suitable gages have been made, although I rely more heavily on my digital micrometer than the track gage.

  • micrometer dials.

  • micrometer collar.

  • micrometer adjustment to the ram stroke which could be altered whilst the machine was in motion.

  • micrometer scale is in the eyepiece it will not change its size.

  • micrometer feed stop.

  • micrometer screw which is used to adjust the distance a spark must jump.

  • The measurement of specimen size with a microscope is normally made by using an eyepiece micrometer.

  • The image is a stage micrometer in 0.01 mm divisions.

  • The RSG is ideally suited for calibrating image analyzer systems and can be used as a high precision stage micrometer.

  • Late model with tumble reverse and compound slide micrometer dials.

  • MICROMETER (from Gr.

  • It became, in fact, essential to invent a " micrometer " for measuring the small angles which were thus for the first time rendered sensible.

  • inventor of the micrometer.

  • The micrometer so mentioned fell into the possession of Richard Townley of Lancashire, who exhibited it at the meeting of the Royal Society held on the 25th of July 1667.

  • 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.

  • The micrometer is at zero when the two edges are brought exactly together.

  • A steel cylinder (about the thickness of a goose-quill), which forms the micrometer screw, has two threads cut upon it, one-half being cut with a thread double the pitch of the other.

  • (1773), p. 190) also gives results of measurements by Gascoigne of the diameters of the moon, Jupiter, Mars and Venus with his micrometer.

  • 16' 24" 16' 16" 8 Gascoigne, from his observations, deduces the greatest variation of the apparent diameter of the sun to be 35"; according to the Connaissance des temps it amounts to 32" 3.3 These results prove the enormous advance attained in accuracy by Gascoigne, and his indisputable title to the credit of inventing the micrometer.

  • Huygens, in his Systema saturnium (1659), describes a micrometer with which he determined the apparent diameters of the principal planets.

  • The Marquis Malvasia in his Ephemerides (Bologna, 1662) describes a micrometer of his own invention.

  • The micrometer of Auzout and Picard was provided with silk fibres or silver wires instead of the edges of Gascoigne, but one of the silk fibres remained fixed while the other was moved by a screw.

  • Beyond the introduction of the spider line it is unnecessary to mention the various steps by which the Gascoigne micrometer assumed the modern forms now in use, or to describe in detail the suggestions of Hooke, 4 Wren, Smeaton, Cassini, Bradley, Maskelyne, Herschel, Arago, Pearson, Bessel, Struve, Dawes, &c., or the successive productions of the great artists Ramsden, Troughton, Fraunhofer, Ertel, Simms, Cooke, Grubb, Clarke and Repsold.

  • Indeed, in those days, the difficulties attached to such measures, and to the measurement of distances with the filar micrometer, were exceedingly great, and must have taxed to the Utmost the skill and patience of the observer.

  • The Modern Filar Micrometer.

  • When equatorial mountings for telescopes became more general, no filar micrometer was considered complete which was not fitted with a position circle.'

  • The use of the spider line or filar micrometer 1 In 1782 (Phil.

  • Dr Hooke made the important improvement on Gascoigne's micrometer of substituting parallel hairs for the parallel edges of its original construction (Hooke's Posthumous Works, p. 497).

  • A still further facility was given to the use of the filar micrometer by the introduction of clockwork, which caused the telescope automatically to follow the diurnal motion of a star, and left the observer's hands entirely at liberty.'

  • The micrometer represented in figs.

  • They are placed at a distance apart less than the focal length of a, so that the wires of the micrometer, which must be distinctly seen, are beyond b.

  • The eyepiece slides into the tube cd, which screws into the brass ring ef, through two openings in which the oblong frame, containing the micrometer slides, passes.

  • The slides are accurately fitted so as to have no sensible lateral shake, but yet so as to move easily in the direction of the greatest length of the micrometer box.

  • Two pins q, r, with spiral springs coiled round them, pass loosely through holes in the forks k, 1, and keep the bearings of the heads in and n firmly pressed against the ends of the micrometer box.

  • One of the most essential points in a good micrometer is that all the webs shall be so nearly in the same plane as to be well in focus together under the highest powers used, and at the same time absolutely free from " fiddling."

  • the micrometer by Trough ton, fitted to their 5 ft.

  • equatorial telescope, is the first position micrometer constructed capable of measuring position angles to 1' of arc.

  • The English micrometer still retains the essential features of Troughton's original construction above described.

  • The later English artists have somewhat changed the mode of communicating motion to the slides, by attaching the screws pdrmanently to the micrometer head and tapping each micrometer screw into its slide.

  • The micrometer represented in fig.

  • 5 is the original Merz micrometer of the Cape Observatory, made FIG.

  • S is the head of the micrometer screw proper, s that of the screw moving the slide to which the so-called " fixed web " is attached, s' that of a screw which moves the eyepiece E.

  • In this micrometer the three slides moved by S, s, and s' are simple dovetails.

  • Another web is fixed parallel to the axis of the screw, as nearly as possible in the same plane with it and passing through the axis of rotation of the micrometer.

  • For the internal structural details of the micrometer the reader is referred to the article " Micrometer " in the 9th edition of the Encyclopaedia Britannica.

  • To use the instrument, it is well first to adjust the web moved by the screw S, so that its point of intersection with the web (commonly called the " position-web "), which is parallel to the axis of the screw, shall be nearly coincident with the axis of rotation of the micrometer box.

  • For this purpose it is only necessary to direct the telescope to some distant object, bisect that object with the movable wire, and read the number of revolutions and parts of a revolution of the screw; now reverse the micrometer box 180° and repeat the observation; the mean of the two readings will be the point required.

  • Now direct the telescope to a star near the equator and so that the star's image in its diurnal motion shall pass across the intersection of the two webs which mark the axis of rotation of the micrometer box.

  • Then, as the diurnal motion causes the star-image to travel away from the axis of rotation, the micrometer box is rotated till the image of the star when at a considerable distance from the axis is bisected by the position-web.

  • The micrometer is now clamped in position-angle by the clamp C, the star again brought back to the axis, and delicate adjustment given in position-angle by the slow-motion screw M, till the star-image remains bisected whilst it traverses the whole length of the position-web by the diurnal motion only.

  • 5) the eyepiece can be made to follow the star for a considerable distance along a position-web parallel to the screw, the bisection of the web by a star moving by the diurnal motion at right angles to the micrometer screw can only be followed for a limited distance, viz.

  • To measure distances with the Fraunhofer micrometer, the position-circle is clamped at the true position-angle of the star, and the telescope is moved by its slow motions so that the component A of the star is bisected by the fixed wire; the other component B is then bisected by the web, which is moved by the graduated head S.

  • The great improvement now introduced into all the best micrometers is to provide a screw s, which, not as in the Fraunhofer micrometer, moves only one of the wires, but which moves the whole micrometer box, i.e.

  • No one, unless he has previously worked without such an arrangement, can fully appreciate the advantage of bringing up a star to bisection by moving a micrometer with a delicate screw-motion, instead of having to change the direction of the axis of a huge telescope for the same purpose.

  • Dawes, who employed a micrometer of the English type (figs.

  • I, 2 and 3), used to bolt the head of one of the screws, and the instrument was provided with a slipping piece, giving motion to the micrometer by screws acting on two slides, one in right ascension, the other in declination, so that " either of the, webs can be placed upon either component of a double star with ease and certainty (Mem.

  • The micrometer shown in fig.

  • micrometer with the upper side of the box removed.

  • S is the head of the micrometer screw, s that of the screw b y which the micrometer box is moved relative to the plate f (fig.

  • The latter are in fact little microscopes carrying a vernier etched on glass, in lieu of a filar micrometer.

  • 9, are cut on the axis of the micrometer screw.

  • The pinion z and the toothed wheel d are connected by an intermediate wheel and pinion Y; the numbers of teeth in the wheels and pinions are so proportioned that twenty-four revolutions of the micrometer screw produce one revolution of the drum and wheel d.

  • 9), (3y is a single rod consisting of two cylinders accurately fitting in the ends of the micrometer box, the larger cylinder being at (.

  • Contact of the web-frame of the micrometer with the side of the box at y would therefore take place, were it not for the micrometer screw.

  • 9) is only prevented by good fitting of the holes 1 3' y'; and, since the weight of the slide is on one side of the screw, misfit here will have the effect of changing the reading for coincidence of the movable with the fixed web in reverse positions of the micrometer.

  • With the Cape micrometer a systematic difference has been found in the coincidence point for head above and head below amounting to o"-14.

  • The short screw whose divided milled head is shifts the zero of the micrometer by pushing, without turning, the short sliding rod whose flat end forms the point d'appui of the micrometer screw at I.

  • a convenient feature in Repsolds' micrometer that the webs are very near the inner surface of the top of the box, so that the eye is not brought inconveniently close to the plate when high powers are used.

  • Another excellent micrometer, originally based on a model by Clark of Cambridge, Massachusetts, has been largely used by Burnham and others in America.

  • Da and The micrometer box, and of course with it the whole system of spider webs, is moved by the screw s, whilst the measuring web is independently moved by the screw S.

  • The method of counting the total number of revolutions gives more friction and is less convenient than Repsolds', and no provision seems to be made for illuminating the micrometer head in the practical and convenient plan adopted by Repsolds.

  • Repsolds' more recent form of the spider-line micrometer (since 1 The marks of varnish so applied will he seen in fig.

  • The micrometer is clamped in FIG.

  • position-angle by the screw K and slow motion in position-angle is given by the screw p. The small drum-head T opposite the micrometer head S turns a screw which acts upon a short cylinder that cannot turn but can move only in the direction of the axis of the micrometer screw.

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