ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 611 



of articulation C ; then a second photograph is obtained on the part A 

 of the plate under an inclination symmetrical with the first. The two 

 views are thus obtained on the same stereoscopic plate in the order in 

 which they should be observed to give the sense of relief, thereby 

 avoiding the necessity of inverting the proofs, which has to be done 

 with an ordinary stereoscope. In certain special cases — e.g. when the 

 relief of the object and the depth of the objective render photography 

 impossible, the photographic image of an object can be replaced by two 

 drawings made with the camera-lucida at different angles ; these two 

 drawings juxtaposed and viewed in the stereoscope give also a good 

 stereoscopic presentation. It is essential that the object should be at 

 the exact level of the axis of rotation C. To obtain this arrangement a 

 method suitable for medium magnifications is to place the object 

 approximately at the level of C, the Microscope tube being vertical ; 

 the tube is then inclined ; if the object no longer remains in the centre 

 of the field, it is either too high or too low, and correction must be 

 made with the micrometric screw^ With high magnifying powers the 

 following method is liest. The objective is first focused on the 

 surface of the stage P, whose coincidence with the plane of the axis is 

 indicated by the index I. Then a preparation, whose thickness is, of 

 course, variable, is placed on the stage P ; the object is thus necessarily 

 higher than C, and must be made to descend by the required amount to 

 the level of C by a movement of the micrometric screw L, the exact 

 focus being at the same time obtained. But the rackwork F must not 

 be touched, nor the original position of the objective modified in any 

 way. 



(2) When the objects to be dealt with exceed 15 mm. the camera 

 is rotated 180° around its rod ; it is then behind and away from the 

 Microscope. Into the tube T a photographic objective of low magni- 

 fying power is now introduced, and the object is arranged on a shelf at 

 the level of C. In this way the enlargement varies from 3"5 to 1. 

 Exactly the same arrangement suffices for the diminution (from ^ to i^j) 

 of too large an object. 



The authors state that, in comparison with ordinary binocular 

 methods, their Microscope yields a photographic field 1*5 to 4 times 

 larger, according to the extension of the bellows. The great value of 

 their instrument, however, consists in the means of stereoscopic photo- 

 graphy with high powers, whereas with binocular Microscopes the 

 photographic enlargement is very limited, inasmuch as their principle 

 depends on the juxtaposition of two equifocal objectives, with necessarily 

 short frontal distance. Moreover, binoculars necessitate photographing 

 on two half -plates, instead of on a single plate of ordinary size. 



Nachet's Oscillating Stag-e for Stereoscopic Microphotography.* 

 A. Guieysse, who was working on this subject simultaneously with, but 

 independently of, MM. Quidor and Nachet, conceived the idea of an 

 oscillating stage, the Microscope, of course, remaining stationary. He 

 .afterwards discovered that, so far back as 1866, Moitessier had hit upon 



* C.R. Soc. Biol, de Paris, Ixiii. (1907) pp. 18, 19 (1 fig.). 

 Od. 16th. 1907 2 s 



