INTRODUCTION. 19 
photographer, or to a manual of photography, for 
detailed instructions with reference to the pro- 
cesses of wet-plate photography, silver-printing, 
etc. Directions will be given, however, for the 
dry-plate process, which offers especial advantages 
for this purpose, and particularly for those who, 
being engaged in other pursuits, can only devote 
a day now and then to photo-micrography. 
The advantages of dry plates are as follows: 
They can be purchased ready for use in such quan- 
tities and of such sizes as may be desired; they 
may be kept indefinitely without deterioration ; 
no time is lost in preparing for work; they are 
more sensitive than wet plates; they can be de- 
veloped at any time subsequent to exposure ; and, 
finally, they do not stain the operator’s fingers. 
The plates which I have used most extensively, 
and with which I have been well pleased, are 
manufactured by the Eastman Dry-Plate Co., of 
Rochester, N. Y. 
Sun-pictures, as compared with hand-work, have 
the advantage of being quickly made, and of be- 
ing absolutely true to nature. The best-executed 
drawings or engravings are commonly more or less 
diagrammatic, and the highest skill is required to 
produce satisfactory illustrations of many of the 
most interesting and beautiful microscopic objects. 
But by photography, the most delicate lines and 
shades are preserved, and one who has no skill in 
drawing is able to make a permanent record of 
what he sees in the course of his microscopical re- 
searches. That is, within certain limits, for not every 
