38 
PRACTICAL PHOTO-MICROGRAPHY. 
carrying the sensitive plate may be raised or lowered, 
and pushed to one side or the other, and this device is 
to be found in later, if not earlier, apparatus. We do 
not lay much stress on the advantage of this arrange¬ 
ment, if the microscope is permanently fixed on the 
apparatus; but if the same microscope is used for 
general observation and for occasional photography, 
then we recommend the rise and fall, and the traversing 
motions, for it is impossible to set down the micro¬ 
scope exactly at the same place always, and the 
slightest deviation from the normal position of the 
microscope will throw the image on the plate con¬ 
siderably out of its normal position. The apparatus 
now under discussion is expensive, but will be found 
to fulfil every desire of the most exacting worker, 
especially with a modification of the focussing device, 
for which the counterpoise system may be recom¬ 
mended. 
We next give a figure and brief description of the 
instrument which we use for our own work, and it is 
the outcome of some years of experiment and frequent 
modification. This instrument (figs. 8, io, and n) was 
made for the writer by Mr. C. Baker, of High Holborn, 
and it leaves little or nothing to be desired in work¬ 
manship, besides being produced at a really moderate 
price. (See Appendix.) 
Here, again (fig. 8), is seen the support for the ocular 
end of the tube ; the body bearing the tube is long and 
strong; there is a rack and pinion for altering the 
length of the tube, which is at its normal a io inch 
