168 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
so that one is able to examine an object under the Microscope as easily 
as if it were standing on the table, quite clear of any photographic 
attachment. 
The pasteboard tube carrying the camera front is, however, fitted on 
to the draw-tube, as, owing to its sm^ll size, it does not interfere with 
the use of the Microscope any more than a micrometer eye-piece or 
other ocular attachment. 
The easiest way to indicate the principles of the method I wish to 
advocate, will be to describe the method in a specific case. 
Say it is desired to obtain a photograph of an object under Zeiss’ C 
with oc. 3, the draw-tube at its full length. 
The object is placed in position, accurately focused, and lighted to 
the best advantage by means of the concave mirror. If great exactitude 
be desired, exact parallelism may be secured by levelling the stage of 
the Microscope and the focusing-screen with a spirit-level. The 
camera, with the bellows hanging loose and unattached, is now swung 
round, so that it is suspended over the Microscope, and fixed at such a 
height that the length from the eye-piece to the focusing-screen may be 
about 8 in. Its front frame is now gently fitted on to the movable 
front already attached to the Microscope. 
If the ground glass be now examined under a focusing-cloth it will 
be found that there is too little light on the plate to enable one even to 
see the position of the object, far less whether or no it is in focus ; but, 
as a matter of fact, it will be nearly so — though, in all probability, the 
error, combined with the difference between actinic and visual foci, will 
necessitate the lens being focused a little away from the object to 
obtain a sharp picture. 
Suppose now we focus the lens out four-hundredths, i.e. two divisions 
of the Zeiss milled head, and, having inserted an Ilford ordinary plate 
in the camera, proceed to expose for about one minute. 
On develojnng the plate, if the lenses used at all correspond to those 
I am using, a very fairly sharp picture will result. 
Now examine the plate closely for any portion of the picture that 
may be in sharp focus, and, having noted this, detach the camera front 
and swing the camera out of the way, and note exactly the number of 
divisions through which the milled head must revolve to bring this into 
sharp visual focus as one looks through the Microscope. 
A few experiments may be necessary before this correction is accu- 
rately obtained; but, once it has been ascertained for any given combination 
of objective, ocular, and length of camera, sharply focused photographs 
may be obtained with far greater certainty than in the ordinary way, 
because it is far easier to focus sharply an object observed in the ordinary 
manner through the Microscope, than when the image is dulled by being 
examined through a ground-glass surface. 
The weaker the objective, the larger will he the correction necessary ; 
for instance, with draw-tube fully out, oc. 3, and a camera-length of 8 in., 
I find that I have for objective A to focus out 25 mm., for B 10 mm., for 
C 4 mm., and for D 2 * 5 mm. 
The exposure, of course, must be increased as the square of tho 
linear amplification or, given that one minute suffice for C, about 3 
