1895 THE MICROSCOPE. 11 



an exposure, and these two points must be put in the 

 optical axis of the objective and ocular you use. For 

 locating this point, cut an old mount and fit it in the 

 plate-holder, like a sensitive plate, obtain its centre point 

 by intersecting diagonals and here make a pin-hole. Put 

 the card-board in your holder, draw both shutters and put 

 the holder in place, closing the bellows up as far as it will 

 go toward the front board, and mark the new board by 

 a long needle put through the hole in the card, and kept 

 perpendicular to the surface of the latter. You may now 

 use the mark on the new front as the centre of a hole to 

 be cut for the microscope tube to enter, and to beat least 

 twice as large as the eye-pieces to be used in it. 



To connect the parts light-tight, make a conical bag of 

 velvet or of similar stuff; the larger end too big to go 

 through the hole in the front, and the smaller end fitted 

 to easily go over the eye-piece of your 'scope, the length 

 being 2i to 3 inches. Pass the bag through the front 

 board and tack or glue its larger end thereto, to be light- 

 tight. The lesser end fits over the eye-piece end and is 

 secured by an elastic band or its equivalent. This gives 

 us a light proof but movable connection between the 

 camera and the microscope. 



To insure the coincidence of the optical axes of the two 

 parts of the apparatus above mentioned, proceed as fol- 

 lows : Having found and marked the centre point of 

 the new front board of the camera, put the microscope 

 in its place on the board, the latter being on a table and 

 made level accurately. 



Now incline the tube of the microscope until horizontal, 

 as shown by a small level placed thereon. Gfently move 

 your 'scope until the eye-piece end presses against a front 

 board, on which you are to trace the outline of its circu- 

 lar milled flange. If you find the hole and circle central, 

 very well ; if not, the microscope as a whole must be 

 raised or lowered until its optical axis is coincident with 



