600 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



arc lamp are readily obtainable. 9, Each, constituent part is capable 

 of an ample range of movement, thus rendering perfect adjustment very 

 simple. 



Fig. 37. — On the left : resistance. In the middle : hood of cover laid back to 

 expose the compensating arc lamp, which travels in exact alignment along 

 runners on the base-board. A lens set in an adjustable sleeve is seen projecting. 



On the right 



adjustable stand for the Microscope. 



(4) PhotomicrograpJiy. 



Wratten Light Filters.* — The Kodak firm have investigated for 

 the purpose of light filters an enormous number of organic dye-stuffs, 

 with which they have been able to prepare a long series of filters of a 

 purity and brightness said to have never before been obtained. These 

 filters are supplied as dyed gelatin film, and are prepared by coating 

 gelatin containing a given weight of dye upon prepared glass, and, 

 after drying, stripping the film from the glass. They are standardized 

 by comparison with a standard whose absorption curve has been 

 measured on a spectro-photometer. The catalogue list comprises nearly 



♦ Wratten Light Filters, Kodak, Limited, London, 1916. 



