OF THE MICROSCOPE. 



163 



The Parabolic Illuminator. This is an instrument 

 intended to accomplish the same end 

 as the spot lens, but in a far more 

 efficient manner. It consists of a 

 block of glass, the outer form of which 

 is a parabola with a cup-shaped de- 

 pression cut in the upper end. It is 

 mounted in a brass fitting, which 

 slides up and down in the sub-stage 

 of the microscope, and thus may be 

 readily adjusted, so as to throw the 

 light properly upon the object. The 



results obtained by means of the parabolic illuminator are 



wonderfully beautiful. 



Polarized Ljight. The micro polariscope consists of two 

 distinct parts, a polarizer and an analyzer, each of which is 

 now generally formed of a Nichol prism properly mounted. A 



Fig. 52. THE PARABOLIC 

 ILLUMINATOR. 



Fig. 53. POLARIZER. 



Fig. 54 ANALYZER. 



common method of mounting the polarizer is shown in Fig. 53. 

 As there shown, the lower ring is intended to slip into the ring 

 of the sub-stage, the rack and pinion of which enables us to 

 place the end of the prism at a proper distance from the object. 

 When the microscope is not provided with a sub-stage, the 

 polarizer is turned upside down, and the brass fitting slipped 

 into a ring, which is attached to the under side of the stage. 

 The milled ring, which is shown uppermost in the figure, 

 enables us to rotate the prism in both cases. 



The analyzer may be arranged in either one of two ways. It 

 may be slipped over the eye-piece, or it may be mounted in a 



