Page:Proceedings of the Royal Society of London Vol 60.djvu/18

10 Table I.—Plate with angle of emergence in air 53° 24'.

Liquid. a —0. a. A. Carbon bisulphide........ 1-6473 24° 15' 53° 26' + 2' a-Bromonaphthalene.. .. 1 ’5341 21 50 53 22 # -1# Benzene........ ............ 1 ’4970 21 0 53 27# + 3# Turpentine................... 1’4726 20 20 53 20# -3# Olive oil...................... 1-4673 20 12 53 21 -3 Glycerol ...................... I ’4934 20 10 53 28# + 4# Chloroform................. 1-4439 19 35 53 19# -4# 1 Alcohol............... .... 1’3561 17 2 53 15 -9 | Water......................... 1-3327 16 21 53 22 - 2 : Table II.—Plate w ith angle of emergence in air 54° 42'. Liquid. a-9. a. A. Carbon bisulphide........ 1-6473 24° 58' 54° 38#' -3#' a-Bromonaphthalene.. .. 1 ’5341 22 35 54 44# + 2# Benzene...................... 1 -4970 21 41 54 44# + 2# Turpentine.................. 1-4726 21 0 54 37 -5 Olive oil........ ............. 1 -4673 20 56 54 45 + 3 1 Glycerol...................... 1 -4634 20 51 54 47# + 5# Chloroform.................. 1-4439 20 17 54 42 0 Alcohol........................ 1-3561 17 45 54 48# + 6# Water......................... 1 -3327 16 54 54 37 -5

that, as would of course be expected, the most accurate results are obtained with liquids of high refractive index, which give comparatively large values of a —6. By determining the values of a.— for each of two optic axes of a given crystal plate, it can easily be ascertained with what amount of accuracy the plate has been cut perpendicularly to the bisectrix.

The principle of the method here described may very possibly be advantageously employed in other branches of optical investigation.

Colour photographs of the spectrum, or of any other object, are obtained by the following method. A transparent photographic film of any kind has to be placed in contact with a metallic mirror during’