190 Prof. Rood on the application 
negatives which present the same appearance under a -_ lower 
magnifying power. 
Positive prints—In order to preserve the fine details, the 
prints should be taken on glass, not on paper; mica answers 
found that a more liberal usg of nitrate of silver and chlorid of 
gold, than is generally recommended makes success easy. 
Magnifying — employed.—To produce enlarged images the 
objectives as is well known may be used alone or in connexion 
he an eye-piece. In the former case with proper illumination, 
sharp images are produced when the distance between the object 
(on the stage,) and the ground glass is as great as five feet. 
With this distance the 
1 inch enlarges 65 diameters. 
bs $ “a “ ace . 
Tn using the objectives in this way the a collar is set ithe 
the microscope is connected with the came 
For more nighly enlarged images it is Bat to add the long 
eye-piece as has been practiced i some experimenters. The 
adj atmo of the screw collar can then be very nearly complet 
before the microscope is connected with the camera, which is 4 
great saving of Bh it will of course fall nearer the mark “un- 
red” than in the first case. However perfectly this opera- 
any may be ieHonned in either instance, allowance must still, 
be made for the actinic focus. By varying the distance between 
the eye-piece and the ground glass different degrees of enlarge 
ment are obtained. When the long, or two inch eye-piece, is 
used, the distance from the object-slide to the eye lens being 12 
inches, from the latter to the ground glass 34 inches, then 
1 inch enlarges 160 diameters. 
4 “ oe 550 “ 
4 “ ti 1 800 6c 
Powers obtained in this way with the two latter objectives have 
y me with advantage. 
Thus with the 1th 118° aperture, ae Wollaston pate of 
44° aperture having a central stop, being as a condenser, 
I obtained sharp negatives: of the P. angulatum aman ed 
