CHAPTER XL 



THE MICRO-SPECTROSCOPE. 



THE micro-spectroscope is used as a means for exhibiting 

 the absence of certain rays of light in a beam which has 

 been modified by its passage through certain substances or 

 solutions. Generally speaking there are two patterns of 

 the instrument, the former made by Messrs. Beck, as 

 shown in Fig. 215, and that 

 made by Mr. Browning, 

 shown in Fig. 216. There 

 is not much difference be- 

 tween the two in actual 

 working, the form the 

 author prefers, however, 

 being that of Mr. Browning. 



The Sorby - Browning 

 instrument consists of a 

 series of prisms, of crown 

 glass and flint, mounted 

 in a small tube, so that 

 they can be removed at 

 pleasure. Immediately be- 

 low this tube is an achro- 

 matic eye-glass ; and below the adjustable slit, placed about 

 the centre of the widened part of the tube, is an ordinary 

 plano-convex field-lens. 



The amount of dispersion, that is, the length of the 

 visible spectrum, is produced by alterations in the prisms, 

 and it is as well for the worker in this branch of micro- 



FIG. 215. 



