46 



THE MICROSCOPIST. 



lines by daylight, or a spectrum of the light transmitted 

 by any object in the field of view. A reflecting prism is 

 placed under one-half of the slit of the apparatus so as to 

 trajftnrit from a side aperture a standard spectrum for 

 comparison. In tfig. 25, A is a brass tube carrying the 

 compound direct-vision system of five prisms and an 

 achromatic lens. This tube is moved by the milled head 



FIG. 20. 



Spectroscope with Micrometer. 



B, so as to bring to a focus the different parts of the 

 spectrum. This is important when the bands or lines to 

 be examined are delicate. D is the stage on which objects 

 for comparison are placed. The light passing through 

 them from the mirror I, goes through a side opening to a 

 reflecting prism which covers a part of a slit in the bot- 

 tom of the tube A. This slit is opened and shut by means 

 of the screws c and H. Fig. 26 shows the internal ar- 



