22 
PRACTICAL PHOTO-MICROGRAPHY. 
time they surely will, they can be tightened up by 
screws. Except a bad fine adjustment nothing is so 
exasperating as a bad coarse one ; a good coarse ad¬ 
justment, on the other hand, is a very great boon. We 
have two microscopes with which we can work com¬ 
fortably, using an “ eighth ” and the coarse movement 
alone—one is a new Student stand by Watson, the 
other is a Powell and Lealand, dated 1866. 
The “ stage ” next requires consideration. The hole 
in it should be of ample size ; a clear inch of diameter 
is not enough, and the stage diaphragms, and even 
iris arrangements, sometimes seen in the stage, 
serve no purpose that we can discover. A 11 mechani¬ 
cal stage is, without doubt, a very great convenience, 
and all hrst-class stands are fitted with one ; but it 
adds to the cost considerably, and it certainly can be 
dispensed with. The photo-micrographer will find a 
good mechanical stage a great boon, chiefly for two 
reasons. F irst, by means of it he can search the 
whole of a preparation without fear of missing any 
part, which cannot be said for the manual practice of 
searching for, say, bacteria with a high power. And 
second, it is easy to mark a spot once found by either 
of two devices. These stages are usually marked with 
two sets of minute divisions at right angles to each 
other, so that a spot once found, the “ reading ” of these 
marks may be noted, and the same spot can be found 
at any future time by simply setting the stage to these 
readings. 
A “ Maltwood ” finder may be used for the same 
