1865.] Sorbt on Spectrum- Analysis applied to the Microscope. 199 



The general construction will be more readily understood by 

 reference to the accompanying Figure 1 : — 



Fig. 1. — Spectrum Microscope. 



The only addition to the microscope itself is the prism (e) and its 

 mounting, shown by the dark lines. This fits into the bottom of the 

 movable tube carrying the achromatic condenser (/). Detached from 

 the microscope is a long narrow slit, shown in section at (b c) ; and 

 the light passing through this at (a) is separated by the prism (e), and 

 passes on to (g), where the image of the slit is seen as a coloured 

 spectrum, on looking through the microscope in the usual manner. 

 By this arrangement we can determine the character of the light trans- 

 mitted by an object placed on the stage at (g), or by one held in front 

 of the slit at (a) ; and, by a little adjustment, we can compare the two 

 spectra side by side. 



2. Description of tlie Instrument. 



Having thus given a general account by way of introduction, I will 

 now describe the apparatus in detail. 



The slit is made of two brass plates about six inches long and one 

 inch broad. The lower has two strips of brass fastened at each end 

 between which the other plate fits, so that it may be moved up and 

 down, and fastened by means of screws, which clamp together the 

 upper part of the strips. The edges of the plates, thus brought toge- 



