762 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 108 shows a new pattern in which these defects are remedied. It 

 will be readily seen that the surfaces of i. and ii. in contact are spherical, 

 and these when cemented together function satisfactorily as a whole. 

 PL XV. fig. 1 shows a photomicrograph of the rays issuing from the 

 condenser. The scale of enlargement is such that the distance between 



\B 



B, 



A 



----- '\P/ 



A 



Fig. 107. 



Fig. 108. 



the ray-crossing and the lower edge corresponds to the thickness of the 

 object-slide. The photograph was taken by means of a fluorescent 

 uranium glass of corresponding refraction. The uranium glass was 

 placed on the mirror condenser, and by means of a drop of cedar oil 



Fig. 109. 



optically connected with it. The view of the rays is lateral, and they 

 proceed from a slit, below the condenser, whose length lies in the plane 

 of the paper. 



Fig. 109 represents a mirror condenser which may be used for dark- 

 ground or for light-ground illumination. It is somewhat larger than the 



