656 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
which is usually damped fast after the camera has been adjusted ; the 
screw of the block n may be loosened, the apparatus swung clear of the 
Microscope about the axis m, a stop adjustment between m and o indi- 
cating the proper position of the camera when swung back. The 
connection between the Microscope and the camera is accomplished by 
means of the usual double collar, but in this case the smaller ring is 
composed of two, the outer sliding over the inner, and having an 
Archimedean screw arrangement. To the outer ring is attached the 
pin p, and by rotating p the outer tube slides forward and enters the 
cap q. When the camera is to be swung away, the tubep is withdrawn, 
and the camera then swings clear. The Microscope is clamped fast to 
the table by a block and screw r. 
The support for the illuminating apparatus consists either of a simple 
prismatic bar, stiffened by a tube as in fig. 159, or of a more complete 
arrangement as in fig. 160. Fig. 159 shows an attachment for acetylene 
gas ; fig. 160 a Thompson 90° arc-light, which is especially suitable for 
photomicrography, as the negative carbon is always in the optical axis, 
so ensuring prolonged centering of the crater. 
Fig. 160. 
The illuminating support shown in fig. 160 consists of a strong brass 
tube fastened to the Microscope table by a bracket, and upon this tube 
are placed the various parts of the illuminating apparatus. The electric 
arc-light may be adjusted for height by rack-and-pinion ; the head of the 
pinion is seen at a. The arc-lamp is supported by a bracket b , and may 
be revolved about a vertical axis at b. The bracket b is fastened to a 
tube which is fitted into the tube of the illuminating bench, which is 
split and reinforced by the clamping ring c. The arc-lamp may be 
swung under the bench by loosening c. 
The various parts upon the bench (i.e the tube) may be adjusted 
vertically by a rack-and-pinion d , and transversely by a slide and screw 
t, t , t. On the upper surface of the tube is cut a longitudinal slot, and 
on each support is a small key e ee, which engages this slot and deter- 
mines the position of the support. The supports are clamped fast by 
the screws h, Ji, Ji, and if it is desirable to dispense with any part of the 
illuminating apparatus, h is loosened, the key e raised, and the support 
swung beneath the bench. 
