674 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



or annular illumination, such appearances are frequently created. Neces- 

 sary as the latter modes of illumination may at times be, they require 

 far more care in interpretation than anything that can be seen with a 



._. " J _ _ _/? i • i i n 



wide cone of light." 



Fig. 158. 



Monochromatic Light Apparatus. — Fig. 158 illustrates the ap- 

 paratus exhibited and described by Mr. C. L. Curties at the Meeting 

 held on May 20th : see ante, pp. 378-9. 



Mace de Lefinay, J. — Projections Stereoscopiques. Joum. de Phys., 1902, p. 311. 



(4) Photomicrography. 



Stereoscopic Photomicrography with Weak Magnification.* — 

 "W. Scheffer's explanation of the theoretical principles underlying the 

 preparation of stereoscopic photographs of microscopic objects are set 

 forth in figs. 159 and 160. The magnification is supposed to be weak, 

 and for such films photographic objectives of short focus without oculars 

 suffice. X, Y are the points intended to be stereoscopically presented 

 in magnification. The objective 0, with the camera and ground glass 

 screen, is first of all set perpendicularly to the object plane (C D, E F, 

 are the planes ; A B, the optic axis). M is the point at which the 

 optical axis of the two positions of the objectives intersect with the axis 

 of the camera. This point must come exactly in the centre of the 

 object ; it is then only necessary to provide for the movement of the 

 objective and of the focussing screens. The camera is first moved to 

 the right and then equally to the left (into the positions M H, M G) ; 

 the result being that projections are received on the screens P' P' and 



* Zeitschr. wiss. Mikr, xix. (1903) pp. 289-96. 



