CHAPTER XVI. 
LANTERN SLIDES. 
F all the forms under which we can show the 
results of photo-micrographic work, none is so 
useful or so striking as a good “ slide ” well projected 
on a good screen. For purposes of demonstration and 
education, no kind of illustration can approach this ; 
the size of the image is great, the details clearly shown. 
Many persons can observe the picture at once, and the 
demonstrator can direct special attention to any detail. 
Moreover, the slides themselves are usually better 
“ prints ” than any on paper, and in almost all cases a 
lantern slide viewed in the hand gives a better repre¬ 
sentation of an object than can be obtained by any 
process of printing on paper, the transmitted picture 
being, in fact, superior to the reflected. And, happily, 
the process of producing slides is by no means difficult 
to learn, the chief desideratum being to know exactly 
what is required, and to know a good slide when we 
see one. 
The first condition of a perfect slide, specially of our 
class of subjects, is perfect clearness of the ground; 
where there is no image the glass of the slide must be 
