472 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
parison of sight with and without these stops teaches. Instead of the 
“entrance-pupils,” here the lower “junction-points,” it is more con- 
venient to apply stops to the “ exit-pupils” or upper “junction-points.” 
The objective lenses are brought together on a small slide working 
sideways with a push motion until the fine-adjustment screw is needed. 
This slide can eventually be fitted with stronger or weaker objectives. 
One of the objectives permits of an in-and- 
out screwing movement, to produce sharp 
definition to the corresponding eye. Com- 
plete presentation to both eyes is an essen- 
tial condition of perfect stereoscopic vision. 
Oculars of different strengths can be fitted. 
The auxiliary apparatus includes, — (A) a 
prism rotator, and (B) a capillary tube- 
stage rotator. 
A. The design and 'working of this little 
apparatus are easily understood from fig. 78. 
The object O is placed on the hypothenuse 
plane of a reflection prism P, so that it is 
exactly perpendicular over the middle of one 
of the two silvered right-angled planes 
When the examination of 0 from above is 
finished, and the observer wishes to examine 
the under side, he has merely to push the 
prism P with the object thereon sideways until O comes under the axis 
A A, and to lower the corresponding tube. A second half-sized, prism 
p, worked also sideways, will give a side view. 
The framework containing these prisms, and the mode of adjusting 
them, is shown in fig. 79, which is fully described in the original paper. 
Fig. 78. 
Fig. 79. 
B. The object of this (fig. 80) is to facilitate observation with the 
highest powers — even with immersion objectives — of minute objects 
which it is desired to view from all points, but whose examination by 
an ordinary method of rotation would be tedious, and to which much 
movement might perhaps be productive of injury. 
A rectangular plate bears in the direction of its long axis a triangular 
channel r, which passes through a circular sunk opening o. The cir- 
