354 : 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
volving stage and the sole plate together, serves in a very efficient 
manner to adjust the position of the revolving stage and the Microscope 
in the two principal directions. A cylindrical guide rod, mounted hinge- 
fashion in a fork at the rear of the sole plate, supports the camera, either 
end of which is adjustable by sliding sleeves fitted with thumb-screws. 
These screws enter w r ith their points into a longitudinal groove running 
along the rod, and thereby keep the camera from turning round. 
A prop at the end of the guide rod maintains the camera in a hori- 
zontal position ; the vertical position is ensured by a stop at the front 
of the rod, a bolt at L acting as a clamp. A pin passed through the 
back of the support obtains the 45° position. 
An optical bench adapted to the front of the sole plate provides 
for the reception of the light-source, condensing lenses, and other 
accessories. 
(4) Photomicrography. 
Winkel’ s New Photomicrographic Apparatus.* — Dr. H. B. Gay- 
lord, of Dresden, describes this apparatus, which is based on Zeiss’ com- 
bined horizontal and vertical camera, and differs from it mainly in 
securing to the operator any inclination of the camera he may desire. 
This is accomplished by attaching the guide rod to a rail which slides 
in a groove made in the sole plate. The two ends of the camera are 
connected by stay-rods, which can be clamped at any angle to a sleeve 
sliding on the guide rod. 
' i (5) Microscopical Optics and Manipulation. 
Aperture as a Factor in Microscopic 1 Vision. | (Plates YII.-X.) — 
Dr. A. Clifford Mercer, in his presidential address before the American 
Microscopical Society in 1896, describes a long series of experiments 
undertaken by him with the view of investigating this subject. 
Considered theoretically and independently as a factor in micro- 
scopic vision, aperture has been almost ignored ; although as an associate 
factor, associated with diffraction by the finer details of microscopic 
objects, it has received no little attention. In this latter form it is the 
basis of the Abbe theory of microscopic vision ; but the writer wishes 
to call attention to some unsatisfactory points in the Professor’s theory, 
and to submit a theory of microscopic vision in harmony with an experi- 
mental study of aperture. 
He believes that the theory of the effect of aperture should be 
applicable to all projecting lenses (e.g. telescopes as well as Micro- 
scopes), explaining resolving power and its limitation ; that the diffrac- 
tion of light by an object should be considered in the same category 
with other changes in direction in incident light produced by an 
object, e.g. those resulting from reflection and refraction ; that diffracted 
and others rays leaving an object in changed directions, as well as rays 
directly transmitted, when travelling the same paths between an object 
and an objective, are affected alike by aperture ; and that the final effects 
in the image experimentally studied by Abbe are the result of changes 
* Zeitsclir. f. wiss. Mikr., xiv. (1898) pp. 313-7 (2 figs.). 
t ‘ An Experimental Study of Aperture as a Factor in Microscopic Vision, 
Buffalo, 76 pp., 4 pis. and 13 figs. 
