The Microscope. 219 



fine cord for adjusting the focus, when the bellows are extended, 

 in the manner hereafter to be described. 



The most important portions of the microscope, however, 

 remain to be noticed, namely the objectives. To obtain the very 

 highest results, these must be of the best quality, and in all 

 powers lower than £ inch, should be supplied with special cor- 

 rections to render the visual and actinic focii coincident. At 

 the same time it may be stated as an axiom that any objective 

 that will give a clear, well defined image of an object under the 

 eye-piece, will also produce a sharp and accurate reproduction 

 of the same upon the sensitive plate. I have made most excel- 

 lent negatives with a French Triplet |, costing no more than five 

 dollars, and magnifying 200 diameters, not equal it is true to 

 the results obtainable with lenses of higher grade and finer cor- 

 rections, but so good, that only a critical eye would discern the 

 difference between them. So let not those possessing only cheap 

 instruments be deterred from entering upon this fascinating 

 branch of photography on that account, as their cheap tools will 

 turn out good work, with the aid of patience and careful manip- 

 ulation. Wide angular aperture is not so conducive to good re- 

 sults as a moderate one. Given good corrections of spherical 

 and chromatic aberrations, good penetrating and defining pow- 

 ers, and the objective of moderate aperture, will defeat its 

 wide angled rival on the photographer's field in every en- 

 counter. 



It may safely be asserted that all powers in ordinary use 

 may be successfully employed in photographing by the aid of 

 ordinary lamp light. I have used them all from 4 inch to l-18th 

 homogeneous immersion; with, and without amplifiers; and all 

 with equally good results. If a selection has to be made by one 

 just purchasing an outfit, I would suggest a 1 inch or | ; \ inch 

 or 4-10th, and l-5th or l-6th. With these and a camera of suf- 

 ficient bellows capacity, a range of powers from about 25 to 250 

 diameters may be obtained; quite sufficient for nine-tenths of 

 the work ever required in this direction. If a higher power be 

 necessary, then a l-10th immersion is recommended. None of 

 these powers from the 1 5th upwards will require any special 

 correction. If they define any given object under the eyepiece, 

 clearly and distinctly, it may be accepted as certain that they 



