XV1II,4. Fitot a. Strobell: Amethodoffocussinginphotomicrography. 423 



found, every step in tlie technique - ■ up to exposing the plate — 

 can be taken without leaving the seat. 



In brief the method is as follows. We bave discarded focus- 

 sing on the ground glass , focussing instead, through a minus 

 spherical lens placed on top of the projection ocular. This lens 

 will give the tbcus required for the ground glass, i. e., the photo- 

 graphic plate; in other words, will cover the distance between the 

 focus through the eyepiece of the microscope and the focus on the 

 ground glass. A series of these lenses ( — 1 ü. to — 10 D.) x 

 furnish the equipment necessary for the magnifications required for 

 practical use (i. e. 1000 diameters or less), with any combination 

 of objective , eyepiece and bellows draw. The lens required for a 

 definite magnification depends upon the eyesight of the Operator, but 

 we have found these variations very slight, and selecting the lens 

 needed by each individual is such.a simple 

 matter, that takiug o n e photograph will 

 settle this point. 



The process of taking a photograph 

 is as follows. With the microscope Stand- 

 ing on the camera base , which rests on 

 a table , select your preparation with the 

 compensating ocular, then replace the com- 

 pensating with the projection ocular. 2 Ad- 

 just the bellows for the magnification 



wanted, and place the minus spherical lens demanded for this magni- 

 fication, on top of the projection ocular, or in the holder for focus- 

 sing lens , which is fastened to the projection ocular by the three 

 screws as shown in the text figure. 3 



J ) A more extensive series is needed if these lenses are to be used 

 for focussing successive planes in <>ne section, as illustrated in our plate. 



-) A projection ocular, however, is not essential -- we have taken 

 just as satisfactory photographs with the compensating oculars — and it 

 is an equally simple matter to select the proper minus sperical lenses for 

 these oculars. 



3 ) This holder we designed to support the lenses and keep them 

 centered over the eyepiece. To have the lens held securely in this way 

 precludes any chance of it falling off, if the table is jarred, and the holder 

 facilitates a rapid change of lenses when taking the focus. This holder was 

 designed for the Zeiss projection ocular — a slight change in the design 

 is needed for the compensating oculars. It costs very little to have the 

 lenses ground to fit the holder and we have found it convenient to keep 



