ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



549 



(3) Illuminating' and other Apparatus. 



New Projection Apparatus for Scientific Work.*— L. B. Elliott, in 

 designing this instrument, has adopted the fundamental principle of a 

 fixed optical centre for all parts of the apparatus, 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, rect- 

 angular in section, having two inclined surfaces, accurately planed, on 



(nz=r> 



E=M 



Fig. 131. 



its upper side, the whole contrivance resembling a fine lathe-bed in 

 rigidity and accuracy of centring. 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 90° by 

 means of the lever A, fig. 131, placing its"" long axis parallel with the axis 

 of the T-slot, when the whole block may be lifted off 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 spring, causing the long 

 axis of the T-piece to assume a position at right angles to the axis of 

 the T-slot. This lever, being actuated by a spring, automatically locks 



* Journ. App. Micr., vi. (1903) pp. 2136-47 (8 figs.). 



