1890.] MICROSCOPICAL JOURNAL. 259 



tached to the ground surface of the screen by means of Canada 

 balsani. 



The camera is mounted upon a stout metal rod, whicli slides into 

 the upright shaft of a very heavy Japanned base, and can be secured at 

 any height to suit that of the microscope (when the latter is inclined 

 to a horizontal position) by means of a milled head. The base is shod 

 with thick felt cloth, so that it may be placed upon any polished table- 

 top without scratching the latter, and at the same time remain firmly 

 fixed in the position it may be placed in. 



And this is all there is of it: Simple, compact, always ready for 

 immediate service, and occupying no appreciable space upon the work- 

 table. Although primarily intended for use with the microscope body 

 inclined to a horizontal position, it may be as readily adapted to the 

 latter in a vertical one, when the character of the objects (as those 

 mounted in fluids) may require. My own method has been to remove 

 the camera from its base and mount it upon the top of an open box 

 containing 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, etc. A correspond- 

 ent in Boston writes me that he has mounted the camera upon a firm 

 retort stand for the same purpose. Many methods of using the instru- 

 ment in an upright position will doubtless present themselves to the 

 worker therewith. 



The illumination may be eflected by reflection from the mirror as in 

 ordinary work, or by removing the latter and placing the lamp behind 

 the stage, and in a direct line with the optic axis. It must be carefully 

 centred in order to illuminate the field alike in all portions. Condens- 

 ers of various kinds, bull's-eye, achromatic. Abbe, etc., can be used as 

 desired, but with moderate and low powers. The best results will be 

 obtained by the employment of simple diaphragms of various sizes to 

 suit, and so placed as to come close as possible to the under surface of 

 the slide upon which the object is mounted. All extraneous light 

 should be excluded so far as possible, 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 will be very greatly shortened by employing 

 direct sunlight as the illuminant, if possible. 



The eye-piece may be removed or not, as the observer may elect. 

 Following after 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 tiie 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 favor 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 are 

 to be made, since the limit of a -|'gth used direct is less than 350^^. 



The corrections of most modern objectives as to visual and actinic 



