-136 Journal of Applied Microscopy 



LABORATORY PHOTOGRAPHY. 



L. B. ELLIOTT. 

 Devoted to Methods and Apparatus for Converting an Object into an Illustration. 



A New Projection Apparatus for Scientific Work. 



Through the courtesy of the Bausch & Lomb Optical Company I have the 

 pleasure of describing for our readers a new model of projection apparatus, 

 designed especially for scientific work. The original model was described by 

 me before the American Microscopical Society at Pittsburg in July last, and the 

 apparatus has, since that time, been improved and an attachment for vertical 

 projection added. 



In the construction of this apparatus an effort has been made to secure the 

 utmost rigidity of the optical parts, the greatest possible facility in changing their 

 position, without changing their relation to the optical center of the apparatus, 

 and to permit the removal and replacement of any part without disturbing any 

 other part, at the same time always insuring perfect centering, no matter how 

 many times removed and returned to the apparatus. 



In the projection apparatus heretofore in general use, portability has seemed 

 to be the main feature which has been kept in view, and rigidity, convenience in 

 working and optical efficiency have been subordinated to this one demand. In 

 the construction of the apparatus to be described no effort has been made to 

 produce a portable apparatus in the ordinary sense of that term, although no 

 undue bulk or weight has been added. I think everyone who has worked 

 with the projection lantern will bear me out in the statement that the greatest 

 amount of time is consumed and the greatest amount of trouble is caused to the 

 operator and the lecturer through the inability to rapidly center the optical parts 

 of the apparatus and to retain the parts in the center, once they have been ad- 

 justed. In this apparatus the fundamental principle of a fixed optical center for 

 all parts of the apparatus has been adopted, the only adjustment required being 

 that to bring the source of light into the optical axis, and to separate it the 

 proper distance from the first element, namely, the rear lens of the condensing 

 system. To this end all the optical parts and their connections are mounted 

 upon vertical pillars attached to heavy steel blocks, which, in turn, are mounted 

 upon a steel bar, rectangular in section, having two inclined surfaces accurately 

 planed on its upper side, the whole contrivance resembling a fine lathe bed 

 in rigidity and accuracy of centering. A T slot is milled in the upper 

 portion of the rod from one end to the other, and in this a T piece attached 

 to a vertical axis passing through the block and carrying the optical parts, 

 is placed. The T piece may be rotated through 9U° by means of the lever 

 A, Fig. 1, placing its long axis parallel with the axis of the T slot, when the 

 whole block may be lifted ofif from the bar, or if removed may be replaced upon 

 the bar and held in position by releasing the lever A, which is actuated by a 



