and Laboratory Methods. 



1371 



The front of the camera is five inches square, and has vertical and horizon- 

 tal movements. The bellows is divided into two, being so constructed that the 

 back part can be taken off the central wooden frame when a short focus is 

 required, and pushed back out of the way. The ground glass and plate-holder 

 can then be fitted into the central frame. Both the back and central frames have 

 vertical and horizontal movements, and are precisely alike in every particular, so 

 that either can be used for focusing and exposing. 



Fig. 5. — Same as Figs. 3 and 4. x 100. Lens B. & L. i in. apochromatic ; 



ocular, y^, inch ; exposure, 2 sec. ; distance of plate 



from hood, 7 inches. 



With regard to the arrangements for locking the optical bench, and mechan- 

 ical focusing, I append a short description. 



In making the mechanical attachment of a photo-micrographic camera for the 

 purpose of operating the fine adjustment of the microscope, two points must be 

 considered, viz. : 



First. An arrangement whereby the attachment can be operated from any 

 position, and 



Second. The operation of the microscope fine adjustment without lost motion 

 or back lash. 



In the camera described above, a third problem is presented, in that the 

 optical bench carrying the microscope and illuminating apparatus is arranged to 

 rotate upon the supporting column, enabling the operator to adjust the specimen, 

 illumination, and preliminary focus before connecting the microscope with the 

 camera. 



It will be seen that this arrangement necessitates the detaching of the focus- 



