176 
Transactions of the Society. 
At the end of the baseboard next the camera is a triangular plate 
of brass, having three holes into which the round feet of the Micro- 
scope (Watson’s H Edinburgh stand) accurately fit, the feet passing 
completely through the holes and resting on the board beneath, which 
is here covered with cloth. At the three angles of the plate are three 
milled screws, passing through holes which (when the screws are un- 
damped) are large enough to allow about a quarter of an inch of free 
movement in each direction. When the Microscope is first put down, 
these screws are released, and the Microscope shifted until it is found 
to be exactly centered. The screws are then firmly clamped, and are 
never again touched. The Microscope can now be instantly put down in 
an accurately central position into the holes which receive the feet, and 
as easily taken up again. This enables the Microscope used for ordi- 
nary observation to be employed for photography with as much ease 
and accuracy as the permanently fixed instrument found in some 
arrangements. 
The small model instrument is preferred, not only because it is 
lighter and more convenient to move about, but also because its optic 
axis when in the horizontal position is lower ; thus the optic axis of 
the whole apparatus, and consequently its centre of gravity, is lower, 
and its stability and freedom from tremor the greatest possible. The 
small light body-tube also confers a greater sensitiveness on the fine 
adjustment than can be obtained in the full-sized instrument ; and it 
will be shown farther on how the small tube may be used, without 
any danger of flare from internal reflection. 
The “turn out” device is dispensed with as being unnecessary 
where the Microscope is not fixed down. All adjustments are easily 
made, with the powerful illumination provided, by projecting the 
image on to a screen of white card. 
The front of the camera has sliding movements in both directions, 
by which the connecting flange can be once for all adjusted to exactly 
meet the eye-piece of the Microscope. Behind it is the usual flap 
shutter for making the exposures, worked by a large milled head out- 
side the camera. 
The focusing arrangement adopted is the one in which an endless 
cord passes over the fine adjustment screw and round two other pul- 
leys below and on each side of it, by which any lateral drag on the 
Microscope is altogether avoided. These pulleys can be changed, and 
used of various sizes, those for high power work being as small as it 
is possible to make them, so that a very slow movement is easily ob- 
tained. The focusing rod passes through the block at the end of the 
camera, and terminates in a large milled head, which, whatever length 
of camera may be in use, is always close to the focusing screen and 
the left hand of the worker. 
In extending or closing up the camera there is only one screw to 
be released, namely, the small one which clamps the focusing pulley 
on to the focusing rod. The clamping screws on the ends of the 
