OF MICROSCOPIC OBJECTS. 203 
photography of magnified objects has evidently no place 
here. 
Few slides caused so much astonishment as these minute 
photographs when first exhibited; small spots were seen to 
contain large pictures, and a page of printed matter was 
compressed into the one-hundredth part of a square inch. 
It would be impossible in this place to give the inquirer 
any instruction in the manipulation of photography, so it 
must be assumed that he already knows this. 
We will first consider the process performed by artificial 
light. The collodion employed in photographing generally 
shows as much structure when magnified as is found in 
linen of moderate texture; but this is not always the case, 
as some samples bear much enlargement without any of 
this appearance. It is evident that a structure so coarse 
would make it entirely unfit for these minute pictures, as 
all the small markings would be destroyed, or so interfered 
with, that no great enlargement would be practicable. To 
obtain almost structureless collodion is not an easy matter, 
and a clever practitioner in this branch of photography 
states that he knows of no method to accomplish this with 
certainty, but he himself tries different samples until he 
falls upon a suitable one, which he then lays aside for this 
object. A beneficial effect is often derived from keeping the 
collodion awhile, but this is not always the case. The slides 
should be chosen of an equal thickness, so that when 
focussed upon one, no re-adjustment may be necessary for 
the others. The glass should, of course, be free from any 
roughness, scratches, or other imperfections, and of very 
good quality and colour. 
The microscope must be placed in a horizontal position, 
and the eye-piece removed, the stage having a small clip 
upon it to keep the prepared plate in position. The nega- 
tive must be supported at a distance from that end of the 
microscope tube from which the eye-piece was withdrawn. 
* This distance will, of course, vary according to the relative 
sizes of the negative and desired picture. With an inch 
