Article contents
XLIII.—On Circular Crystals
Published online by Cambridge University Press: 17 January 2013
Extract
In 1836, Mr Fox Talbot communicated to the Royal Society a paper “On the Optical Phenomena of certain Crystals” which he obtained by dissolving a crystal of Borax in a drop of somewhat diluted Phosphoric acid. When the acid and the salt are in proper proportions, “the field of view of the microscope is seen covered with minute circular spots, each of which is like a tuft of silk radiating from a centre, and is composed of a close assemblage of delicate acicular crystals forming a star.” Among these crystals are seen interspersed “a number of circular transparent bodies, which are tufts or stars of acicular crystals, in such close assemblage as to be in optical contact with each other, and to produce the appearance of a single individual.”
- Type
- Research Article
- Information
- Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 20 , Issue 4 , 1853 , pp. 607 - 623
- Copyright
- Copyright © Royal Society of Edinburgh 1853
References
page 607 note * Fig. 120 in the New Edition, just published.
page 607 note * Phil. Trans., 1815, p. 49, 38; and 1816, p. 97.
page 608 note * This method consists in placing a film of selenite (sulphate of lime) between the polariser and the substance to be examined. If the polarising structure is produced by circular crystals, it will appear covered with spots, or minute sectors, of two different colours, the one being a tint a little lower, and the other a tint a little higher, than that of the selenite. The higher tint is the sum of the tints of the two substances, and the lower their difference, the tint of the selenite being increased by that of two of the sectors, and diminished by that of the other two.
page 613 note * Treatise on Light, § 770, Figs. 155, 156, 157, Plate IX.
page 614 note * In making these observations, and on many other occasions, I have felt the great inconvenience of the present, and in general, perhaps the best, arrangement of the compound microscope. High powers being always obtained by object-glasses of short focal length, it is almost impossible, in transparent structures, to develope them, when they consist of lines or parts of different thickness. Vision is destroyed by the refractions and diffractions of the intromitted light. The only remedy for this is to use ½-inch, or even 1 or 2-inch object-glasses, and obtain the power that is required at the eye-piece, by means of grooved and other lenses of diamond, garnet, &c.
page 619 note * Stearine gives the same polarised halos as oil of mace.
page 622 note * Discoveries in the Ruins of Nineveh and Babylon. By Austen H. Layard, M.P. Appendix, p. 674–676.
- 8
- Cited by