260 SUMMARY OF CURRENT RESEARCHES RELATING TO 
taming the Microscope. An opening in the top of the box allows the 
cone to be slipped over the tube of the Microscope, and in this manner I 
have made very successful negatives of blood-corpuscles in rouleaux in 
their own serum, yeast spores in fluid, &c. A correspondent in Boston 
writes me that he has mounted the camera upon a firm retort-stand for 
the same purpose. Many methods of using the instrument in an upright 
position will doubtless present themselves to the worker therewith. 
The illumination may be by reflection from the mirror as in 
ordinary work, or by removing the latter and placing the lamp behind 
the stage in a direct line with the optic axis. It must be carefully 
centered in order to illuminate alike in all portions. Condensers of 
various kinds, bull’s-eye, achromatic, Abbe, &c., can be used as desired, 
but only with moderate powers. The best results will be obtained 
by the employment of simple diaphragms of various sizes to suit, and so 
placed as to come as close as possible to the under surface of the slide upon 
which the object is mounted. All extraneous light should be excluded 
and none be allowed to enter the objective other than the rays which 
illuminate the specimen. Opaque objects may be photographed quite as 
successfully as transparent ones, but the time of exposure would be 
very greatly shortened by employing direct sunlight. 
The eye-piece may be removed or not, as the observer may elect. 
Following the teachings and practice of the late Dr. J. J. Wood- 
ward, I have almost invariably worked without it, using an amplifier 
where sufficient magnification could not be obtained with the objective 
alone. In using medium and high powers, I have not found the eye- 
piece objectionable, but with low powers it certainly detracts from 
sharpness of definition, so that my preference is decidedly in favour of 
the amplifier where an increase of power beyond that obtainable with the 
unaided objective becomes necessary. If possible, however, always use 
the latter alone. The short tube-length, alone possible (when using the 
“ Handy ” camera), renders the employment of amplifier or ocular 
necessary, if enlargement beyond three or four hundred diameters is to 
be made, since the limit of a 1/18 used direct is less than 350°. 
The corrections of most modern objectives as to visual and actinic 
foci, are so nearly identical that no difficulty will be experienced in 
obtaining sharp definition of any subject if a little care be used. But it 
may not be amiss to say the student’s series of Bausch and Lomb are the 
best, by all odds, of any I have ever seen or used at all approaching 
them in moderation of cost. I have numerous remarkable examples of 
their work which I have never seen excelled by lenses of equal powers, 
no matter what their cost. It certainly is not necessary to go abroad in 
these latter days to get the best in the optical as well as in many other 
directions. 
The dry plates for the “ Handy ” camera are furnished by the makers 
in two degrees of sensitiveness to suit every variety of subject. They 
are readily developed by any of the methods used for gelatin plates, 
my own preference being given to hydroquinone or a mixture of that with 
cikonogen, as giving the clearest results, clearest details, and sharpest 
contrasts with any desired amount of deusity. Their cost is but 25 cents 
per dozen, certainly cheap enough to tempt any one to their use. 
In conclusion, a few words upon various printing methods. Pre- 
