J. RHEINBERG ON COLODEBD ILLUMINATION. 347 



carrier cause the background to be coloured, whilst those which 

 can be pulled out from the right side cause the object to be 

 coloured. 



The number of effects which can be obtained with such an 

 apparatus is unlimited. Mr. Rousselet showed us some weeks 

 ago an. ingenious colour illuminator, by which, according to a 

 little mathematical calculation, 36 effects could be obtained. 

 By applying a similar calculation to this arrangement it would 

 give 19 18 power, or some few hundred millions of combinations. 

 This number may be too much even for an enthusiast, and I 

 prefer to pass over from the quantitative to the qualitative use 

 of the arrangement. 



I venture to think, Mr. President, that for simplicity in use 

 it cannot be excelled, as it allows of every kind of illumination 

 and stop being automatically brought into action whilst the 

 object is under examination. The best result can, therefore, be 

 obtained with far greater rapidity thau ordinarily, and com- 

 parisons can be effected without having to bother about taking 

 stops in and out, as in the ordinary way. The apparatus in my 

 hand, although efficient, is of course needlessly clumsy and 

 heavy. Apart from the brass box, 1 made it myself, to fit my 

 own instrument. I believe, however, the principle can be easily 

 adopted in a neater form, and made to tit any condenser. 



