Great refracting telescope, presented by the emperor Alexander I.
It is a colourless, highly refracting liquid, boiling at 78°; it fumes on exposure to moist air.
In it are, moreover, enclosed unicellular glands pouring their highly refracting contents, of a more or less rod-like shape, directly to the exterior.
The more highly organized species have often very numerous eyes (Amphiporus, Drepanophorus), which are provided with a spherical refracting anterior portion, with a cellular " vitreous body," with a layer of delicate radially arranged rods, with an outer sheath of dark pigment, and with a separate nerve-twig each, springing from a common or double pair of branches which leave the brain as n.
Besides these more highly differentiated organs of vision, more primitive eyes are present in others down to simple stellate pigment specks without any refracting apparatus.
Such an instrument consists of a triangular prism set with its refracting edge vertical on a rigid platform attached to a massive stand.
These are of dense flint-glass (Schott 0.102), and each has a refracting angle of 63° 29'.
On the other hand, that the direction of complete polarization should be independent of the refracting power of the matter composing the cloud has been considered mysterious.
The crystals are feebly doubly refracting, and in polarized light exhibit a banded structure parallel to the cube faces.
Lehmann it melts at 168° (or at a slightly lower temperature in its water of crystallization) and on cooling forms optically isotropic crystals; at 125.6° the mass becomes doubly refracting, and from a solution rhombohedral (optically uniaxial) crystals are deposited; by further cooling acicular rhombic crystals are produced at 82.8°, and at 32.4° other rhombic forms are obtained, identical with the product obtained by crystallizing at ordinary temperatures.
In their natural condition the marekanite spheres are doubly refracting, but when they have been heated and very slowly cooled they lose this property and no longer exhibit any tendency to sudden disintegration.
An admissible error of phase of 4X will correspond to an error of IX in a reflecting and 2X in a (glass) refracting surface, the incidence in both cases being perpendicular.
It is a colourless, strongly refracting liquid, which boils at about 220° C., slight decomposition setting in above 150° C. Water decomposes it with production of leucone.
Benzene is a colourless, limpid, highly refracting liquid, having a pleasing and characteristic odour.
If p" is the refracting angle of the prism, and n the magnifying power of the eye-piece, then p"ln will be the distance observed.
3) refracts upwards, while the prism Q, which has its refracting edge perpendicular to that of P, refracts towards the right.
If the refracting angleof the prism is small, then the ratio of the dispersion to the mean deviation of the two rays is the dispersive power of the material of the prism.
This shows that the connexion between the refrangibility of light and its wave-length does not obey any simple law, but depends on the nature of the refracting medium.
This, however, is not the case with ordinary refracting media, the refrangibility generally increasing more and more rapidly as the wave-length diminishes.
In studying the dispersion of the aniline dyes, a prism with a very small refracting angle is made of two glass plates slightly inclined to each other and enclosing a very thin wedge of the dye, which is either melted between the plates, or is in the form of a solution retained in position by surface-tension.
Only very thin layers are sufficiently transparent to show the dispersion near or within an absorption band, and a large refracting angle is not required, the dispersion usually being very considerable.
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.
There are three refracting angles possible, one of Ito° between two adjacent prism faces, one of 60° between two alternate prism faces, and one of 90° between a prism face and the base.
Mariotte explained the inner halo as being due to refraction through a pair of alternate faces, since the minimum deviation of an ice-prism whose refracting angle is 60° is about 22°.
As the sun rises, the rays enter the prisms more and more obliquely, and the angle of minimum deviation increases; but since the emergent ray makes the same angle with the refracting edge as the incident ray, it follows that the parhelia will remain on the parhelic circle, while receding from the inner halo.
In Germany and elsewhere refracting theodolites and transit instruments are sometimes employed.
The substance is usually optically isotropic, though sometimes it exhibits anomalous double refraction; fibrous zinc sulphide which is doubly refracting is to be referred to the hexagonal FIG.
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.
Prop. 3) "that all refracting substances diverged the prismatic colours in a constant proportion to their mean refraction"; and he drew the natural conclusion "that refraction could not be produced without colour," and therefore "that no improvement could be expected from the refracting telescope" (Treatise on Optics, p. 112).
The first person who succeeded in making achromatic refracting telescopes seems to have been Chester Moor Hall, a gentleman of Essex.
He argued that the different humours of the human eye so refract rays of light as to produce an image on the retina which is free from colour, and he reasonably argued that it might be possible to produce a like result by combining lenses composed of different refracting media.'
In most cases refracting and reflecting systems are arranged so that the natural interpupillary distance is reduced.
That this is not a necessary characteristic of light was discovered by Christian Huygens, who found that, whereas a stream of sunlight in traversing a rhomb of spar in any but one direction always gives rise to two streams of equal brightness, each of these emergent streams is divided by a second rhomb into two portions having a relative intensity dependent upon the position with respect to one another of the principal planes of the faces of entry into the rhombs - the planes through the axes of the crystals perpendicular to the refracting surfaces.
Examining the light reflected from the windows of the Luxemburg palace with a doubly refracting prism, he was led to infer (though more refined experiments have shown that this is not strictly the case) that light reflected at a certain angle, called the polarizing angle, from the surface of transparent substances has the same properties with respect to the plane of incidence as those of the ordinary stream in Iceland spar with respect to the principal plane of the crystal.
Malus that the interposition of a doubly refracting plate between a polarizer and an analyser regulated for extinction has the effect of partially restoring the light, and he used this property to discover double refraction in cases in which the separation of the two refracted streams was too slight to be directly detected.
The phenomena of chromatic polarization afford a ready means of detecting doubly refracting structure in cases, such as that produced in isotropic bodies by strain, in which its effects are very minute.
In the contrary case, total reflection commences as soon as sin i =µ 1, µ being still the relative refractive index of the more highly refracting medium; and for greater angles of incidence r becomes imaginary.
Applying this interpretation to the formulae given above, it follows that when the incident light is polarized at an azimuth a to the plane of incidence and the second medium is the less refracting, the reflected light at angles of incidence exceeding the critical angle is elliptically polarized with a difference of phase A between the components polarized in the principal azimuths that is given by tan (A/2) =cot i l l (1 - µ 2 cosec 2 i).
Thus if A = 42, p. must exceed 7r/8 or 2.414, that is, the substance must be at least as highly refracting as a diamond: if A =7 /4, µ must be greater than 37r/16 or 1.4966, and when this is the case, it is possible by two reflections to convert into a circularly polarized stream a beam of light polarized at 45° to the plane of incidence.
504), who has found the remarkable result that copper, gold, magnesium and silver have refractive indices less than unity, and this has been completely confirmed by observations with metallic prisms of small refracting angle.
This is a plate made of two equal wedges of quartz, that can be moved over one another so as to vary its thickness, and are cut so that the faces of the plate are parallel to the optic axis, which in the first wedge is perpendicular and in the second is parallel to the refracting edge.
The high excellence of the s sle data collected by them was a combined result of their skill, and of the vast improvement in refracting telescopes due to the genius of Joseph Fraunhofer (1787-1826).