Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1845 edition. Excerpt: ... Talbot's "Analytic Crystals." As these experiments, however, are full of interest, I have judged it advisable to extract from the Philosophical Transactions, and give entire, in the Appendix, Mr. Talbot's own papers upon the subject. If, in place of the upper prism, or analyzer, a doubleimage prism be fixed at P, another and very beautiful series of effects will result from the exchange. With this modification there will at the same instant be seen two images of the object arrayed in their complementary colours; and if we turn this prism round in the manner before described, an interchange of colours will take place between the images, the one assuming that of the other. If long needle-shaped crystals are procured for the purpose, the two images will be so far separated as to appear quite distinct. They will vary in their positions also, as well as in their colours and intensity, while the prism is being turned. A moon-shaped or crescent form of complementary colours will be discernible on each side of the field of view, while the latter will be white, from the union of the two complementary colours. The most gorgeous effect of all, however, is produced by this double-image prism when a plate of quartz is inserted below the crystals (say crystals of chlorate of potass) placed at a, b. In short, the whole experiment is so beautiful, that it is in vain to attempt any thing like a description of it. Some crystals possess the peculiar property of exhibiting two colours, when viewed by polarized light; the one being elicited by the ordinary, and the other by the extraordinary ray. Hence they are termed dichromatic. To display dichroism in crystals, the lower prism, or polarizer, should alone be used; the eye-piece being allowed to remain as...
