98 ELEMENTARY CHEMICAL MICROSCOPY 



feeding and moving them are in the ratio 2:1. Hence the move- 

 ment through the key N 2 compensates for the more rapid con- 

 sumption of the horizontal carbon. 



The projection eyepiece in C forms an image upon the ground 

 glass or photographic plate of the camera U, the size of the photo- 

 graph taken being regulated by extending or contracting the 

 bellows of the camera. A graduated scale engraved upon the 

 optical bench, upon which the camera slides, permits a record 

 being kept of the position of the photographic plate at the time 

 of the exposure. In order to obviate the necessity of passing to 

 the rear of the camera to look at the ground glass and to focus, 

 a mirror is placed within the camera box and hinged to one cor- 

 ner; by means of the lever I this mirror may be swung diagonally 

 across the box at an angle of 45 degrees. The image of the 

 preparation will thus be projected upon this mirror whence it is 

 reflected upon the glass g. The investigator can thus examine 

 the image and focus the same without leaving his seat before the 

 body tube T. When an exposure is to be made, the lever / is 

 pushed back until the mirror lies flat against the side of the 

 camera. There is thus an unobstructed passage through C and 

 the camera to the photographic plate. 



Although the Reichert metallurgical microscope is one of the 

 best and most convenient of its kind, it has at least one very 

 serious defect. It is supplied with specially constructed objec- 

 tives whose mounts are of small diameter so made as to drop 

 into a sleeve or adapter instead of screwing in as is the case with 

 ordinary objectives. The purchaser of the instrument must 

 therefore obtain his entire outfit of objectives at the time the 

 microscope is bought. If future purchases of objectives are 

 required it is necessary to obtain them from Reichert and in 

 order to be certain of their proper centering the microscope 

 should be sent to factory. 1 



1 This difficulty has been eliminated in the instrument in the author's laboratory 

 by fitting the opening above the illuminating prism with standard or international 

 thread ("society screw"), thus permitting the use of all standard objectives irre- 

 spective of the firm manufacturing them, and thus greatly increasing the usefulness 

 of the microscope, particularly when the instrument is employed for the examina 

 tion of transparent objects by transmitted light. 



