1893.] THE MICROSCOPE. 23 



the object we are photographing, the objective in the experi- 

 ment, and upon the illumination. 



I would advise every one to keep a record of each and every 

 trial, and be content if at first one good scientific negative is 

 secured out of every half dozen used. I can do no better in 

 answering the above question than to present the results of my 

 experience gathered from a record like the one just recom- 

 mended. 



By using the camera I have described and with Carbutts' 4x5 

 keystone, blue label, lightning plates, the good results with the 

 several objectives described below are given : 



Without Condenser. 



Leitz, No. 1, in sunlight. ^ second; in lamplight. ^ seconds. 



B. &. L., professional, three-fourths, in sunlight, 4 seconds ; 

 in lamplight, 20 seconds. 



B. & L., student, one-half, in sunlight. 6 seconds ; in lamp- 

 light, 30 seconds. 



With Condenser. 



B. & L.. professional, one-fifth, in sunlight, 5 seconds; in 

 lamplight, 1^ minutes. 



Leitz, No. 7, in sunlight, 10 seconds ; in lamplight, 3 minutes. 



Queen & Co., one-fifteenth, N. A. 1.30, in sunlight, 30 

 seconds ; in lamplight. 10 minutes. 



The lamplight negatives were all taken with the Acme lamp, 

 using the bull's eye attached to the shade, and placed from eight 

 to fourteen inches from the object, the mirror, of course, being 

 turned aside. 



The objects used in the above experiments were various, but 

 consisted mostly of sections of animal and vegetable tissue, parts 

 of insects, diatoms, blood corpuscles, bacteria, and the like. 



After making the exposure the negative must be developed, 

 and with every dozen, or half dozen, plates there are printed 

 directions, which it is best to follow closely. The different 

 manufacturers have formulas which differ in some minor points, 

 but these formulae are best adapted to the several plates used. 



Two principal developers are recommended, known as the 

 pyro and hydrochinon. Equallv good results may be obtained 

 from the use of either of these, if the proper exposure has been 

 made. The pyro develops quicker than the hydrochinon, but 

 the latter can be used over and over again, while the pyro needs 

 to be fresh. Personally, I have had the best results in photo- 

 micrography bv using hvdrochinon, and I would advise every 

 one to try it. There is no danger of over-developing or fogging 

 the picture, and it does not need to be so closely watched as the 

 pyro developer. If a negative is suspected to have been over- 



