Light; a course of experimental optics, chiefly with the lantern . both sides a piece of card in whichare cut holes too small for the crystal to fall through. The ends of thebrass are better bent away from the stage. Crystals cost 3^-. to $s. each. 2 At this stage the lamps had better be removed till it is seen howthings go. The metal slide will probably have taken up sufficient heatto go on further without more; and a very moderate excess of heatwill calcine the clear crystal into mere plaster of Paris. - Y 2 324 LIGHT. IcHAP. direction. On the lamp being removed the whole processis reversed.
Light; a course of experimental optics, chiefly with the lantern . both sides a piece of card in whichare cut holes too small for the crystal to fall through. The ends of thebrass are better bent away from the stage. Crystals cost 3^-. to $s. each. 2 At this stage the lamps had better be removed till it is seen howthings go. The metal slide will probably have taken up sufficient heatto go on further without more; and a very moderate excess of heatwill calcine the clear crystal into mere plaster of Paris. - Y 2 324 LIGHT. IcHAP. direction. On the lamp being removed the whole processis reversed. 172. Conical Refraction.—A more surprising proofof the reality of these wave-shells was discovered by SirW. Hamilton, On projecting them according to this theory,they were found to resemble those partially shown in (from Miiller-Pouillet). Now if a single ray traversesthe crystal in the line p p, or p p, on reaching the surface itis refracted into air, as usual, from the perpendicular. Thatperpendicular has reference to the (angetifs of two different. Fig. 185.—Bi-axial Wave-Shells. curves, and so produces two different refractions. If theshells are completed, however, as in a solid model, it isfound that the four points p are cusps, or hollows resemblingthat surrounding the stem- of an apple; and it thereforefollows that pn emergence from the point p, the ray mustbe spread out into a diverging conical shell of rays. Here,therefore, was a mathematical prediction of a phenomenon ? It is very difficult to give a clear idea of tlig complicated in bi-axials to ordinary readers. Some may derive assistance-from another and differently shaded figure, which will be found underthe article Undulatory Theory, in Chamberss Cyclopaedia, XV.] CONICAL REFRACTION. 32s never foreseen by Fresnel, who had confined himself to thesingle plane through the points p shown in the diagram ;and such a kind of refraction was not only opposed to ^11experience, but to all appare
Size: 1413px × 1769px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidcu3192403121, bookyear1882
