108 



On " The Chromatoscope," A Method of Illuminating 

 Crystals and Similar Objects by Coloured Light. 



By J. D. Hardy. 



{Communicated Apeil 28th, 1882.) 



I wish to introduce to your notice tins evening a new method of 

 illumination which will be found of great value in mineralogy, 

 crystallography, and on all such material where polarization cannot 

 be applied; and even with objects which will polarize this method is 

 equally applicable (unless it is in experiment or study). It differ- 

 entiates some objects almost as well as polarization, while the light 

 or brilliancy is much greater, giving to them a beauty and clearness 

 such as have not yet been attainable. I show it here in its simplest 

 form, but it is capable of many modifications, and its cheapness as 

 a substitute for the polarizing apparatus will render it applicable 

 to the cheapest microscopes with very little additional expense. 



The construction is as follows : — Taking a spot lens, a short 

 flanged tube is fitted to slide easily inside, and underneath 

 the " spot " when attached to the microscope. I cement a piece 

 of clear glass to the flange (or it may be bevelled in), and to the 

 inner side of the plain glass I put two or three pieces of stained 

 glass, either kept in their places with a little balsam or by another 

 piece of plain glass above them, as in a kaleidoscope. This com- 

 pletes the instrument, which, it will be seen, is as simple as possible. 

 The light is transmitted by the mirror in the usual way, and 

 the revolution of the " Chromatoscope " will show the same 

 effect on crystals, &c, as if they were polarized. Such objects 

 as Sponge spicules, Polycistina, Diatoms, &c, have all their 

 peculiarities rendered more easily visible, and at the same time 

 their appearance is greatly enhanced by the effect of a variety 

 of tints which are not otherwise obtainable. Another advantage 

 is, that crystals can be viewed as if polarized, without being 

 damaged by mounting in balsam, or having a cover-glass over 

 them. The finest spicules of some crystals are thus kept intact, 

 and exhibited with great clearness. 



