and Laboratory Methods. 



2137 



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 the block on the rod, preventing accidental overturn- 

 ing during adjustment. The block, with whatever optical apparatus it may 

 carry, now rests upon the two inclined surfaces of the bar, and may be slid 

 along its length, permitting whatever adjustment is required, and when in proper 

 position the lever B is depressed, locking the whole rigidly upon the bar by 

 means of a cam which draws the T piece firmly against the top of the T slot. 

 It will thus be seen that any part of the optical equipment can be removed 

 from the apparatus, or replaced, by releasing the T piece through the 

 operation of the lever B, and rotating the lever A through 90°, and that each 



cn 



^.1 



Fig. 1. — Detail of construction of base blocks for apparatus sup- 

 ports showing the two inclined planes on which the blocks rest. 

 .S" piece in 7" slot which, when rotated 90° by the lever .1, per- 

 mits the removal of the base block from the rod ; also the 

 clamping lever />', which clamps the base block rigidly on the 

 rod A'. 



element will always return exactly in the optical axis, since its support rests only 

 on the two inclined surfaces of the rod R, and must in every case find the true 

 center through the clamping action of the cam lever B. The rigidity of the steel 

 bar R and the heavy construction of the base blocks and vertical supports of the 

 optical part retains the alignment and centering. Adjustment is made for the 

 original centering of the optical parts in the vertical plane by mounting them 

 on rods which slide in the sleeve tube S, and when centering has been accom- 

 plished further motion is prevented by the thumb-nut T, which is clamped 

 tightly, and which should, therefore, never be touched unless the part is decen- 

 tered through some accident. In order to make all parts convenient for mani- 

 pulation and interchangeable for different classes of work, the bellows, lens 



