MICROGRAPHS AND MOUNTING THE PRINTS WITHOUT CUTTING. 293 



For convenience in working, Mr. Curteis has made for me 

 a small piece of apparatus which screws into the nose-piece 

 of the microscope, and is itself of the nature of a secondary- 

 nose-piece, to facilitate the changing of the stops. It is fitted 

 with a swing- out arm, carrying a ring which holds the stops 

 and w T hich revolves through 180° exactly, thus changing the 

 aperture in the stop from one side of the optic axis to the 

 other, for the purpose of making the two exposures. Except 

 for this revolution of the stop, the two photographs are 

 taken without any alteration whatever in focus, illumination, 

 position of object or apparatus, except, of course, the dry 

 plate. 



To obtain the two pictures on one plate in the correct position 

 for printing and mounting without cutting, I use what is known 

 as a repeating back. One picture is taken at a time, that on 

 the left half of the plate with the aperture in the stop to the 

 left of the optic axis, and that on the right half of the plate 

 with the aperture in the stop on the right of the optic axis. 

 The images are now on the negative in the correct positions 

 for printing and mounting without any further trouble. This 

 description is correct for the |-in. objective and all lower powers, 

 used with an eye-piece, but may possibly have to be reversed 

 with higher powers. 



In conclusion, I should like to add that particular care must 

 be taken in fitting the nose-piece so as to ensure the true hori- 

 zontal alignment of the apertures when the stop is revolved 

 from one side of the optic axis to the other. If the apertures 

 are not truly aligned, the finished prints will not superimpose 

 properly, and will not be clear and sharp. I may, perhaps, 

 also mention that my only trouble has arisen from a difficulty 

 in obtaining equal illumination of both pictures with transparent 

 objects by transmitted light ; but as my photographs have been 

 taken without an optical bench, this difficulty may not arise 

 when one is used. 



