314 
Transactions o f the Society. 
cell and have not once noticed a want of coincidence of visual and 
actinic foci. Further, I have focused with lamplight not passing 
through the blue cell, and then photographed with the blue cell in 
place with a result quite inferior to the next, the next being obtained 
under the same conditions excepting that the blue cell was in place 
when focusing. The use of the blue cell in focusing secures excellent 
results with the Wales photo-objectives, corrected for the violet ray. 
After passing through the blue cell the light is received by a substage 
condenser and focused on the object. My substage not only carries 
ordinary Powell and Lealand achromatic condensers for high power 
work, but by means of adapters also carries, instead, an eye-piece or 
a suitable objective as a condenser for low-power work. 
The round table-top expansion (figs. 35-37) is divided by degree 
markings, enabling me to turn the board supporting the lighting 
Fig. 37 . 
apparatus to any required angle for oblique illumination of transparent 
objects, or so far around as to cause the light to fall at suitable angles 
on opaque objects. That end of the revolving board which is under 
tbe Microscope is circular. The upper surface of the circular 
portion presents two levels, a central circular higher level surrounded 
by a peripheral lower level. On the latter rest the three feet of the 
Microscope tripod, in such fashion that when the two feet away from 
the camera, or under the substage, are snugly against the edge of the 
central raised level, the object on the stage is in the vertical axis 
about which the board revolves. Therefore, after the board has been 
turned out of line for oblique illumination, the Microscope can be 
placed in new correct position immediately, by bringing tbe two feet 
mentioned against the edge of the higher level, and the eye end of the 
