l'ltoro^tlCROGR.■tr!ly .ixd rr.ciiNiCAL microscopy hi 



scopic mount ; ami fur stiKl\iny; tlie I'lTcct of ilycs or stains on ct-rtain 

 types of transparent mounts. For tlie purpose of filter studies the 

 Hiiger wave-length spectrometer constitutes a very useful accessory. 

 This instrument is illustrated in I'ig. it, and in Fig. 10 is shown hy 

 direct color photography the residual light from an arc lamp after 

 passing through various filters. The s(K'ctrometer is adapted for 

 either direct vision work or photography, a camera and telescope 

 l)eing interchangeable. Instruments for ol)servation with spectro- 

 scopically deconifxiseil light constitute what are known as spectro- 

 scopic eyepieces and are ver\' useful for certain classes of work, since 

 they replace the usual microscopic e>epiece and may be used with 

 any objective. Precision instruments of this type are capable of 

 miMstiriiii; the transmission or absor|)lion spectrum of \ery minute 



Kig. 11 — .\ six'ctroscopic eyepiece by Zeiss. This instrument replaces the usual 

 eyepiece of tlie microscope when it is desired to make observations with sjjectro- 

 scopically decomposed light. It yields an image of the transmission spectrum of the 

 object with a supcrimposetl .•\ngstroni scale and if desired the transmission spectrum 

 of the staining reagent may also l)e brought into the field of vision. The staining 

 reagents are placed in glass vials. 



bodies such for example, as a single bUxjd corpuscle, which state of 

 perfection is said to be attained by the Zeiss instrument, illustrated 

 in Fig. 11. 



The wave-length of the light used in photomicrography also has 

 other useful functions to perform and for some classes of work these 

 take precedence. Mention has been made of the correction of objec- 

 tives for al>erratif)ns which are inherent in the simple lens. When 

 an objective, not fully cf)rrected, is used for photomicrography at 

 the higher magnifications, color distortions as.sert themselves and 

 result in faulty performance of the objective unless filters are used 



