550 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the block on the rod, preventing accidental overturning during adjust- 

 ment. 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 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 centre 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 



Fig. 132. 



retain the alignment and centring. Fig. 131 shows the details of con- 

 struction of the base-blocks for apparatus supports with the two inclined 

 planes on which the blocks rest. S is the piece in T-slot which, when 

 rotated 90° by the lever A, permits the removal of the base-block from 

 the rod ; B is the clamping lever, which clamps the base-block rigidly 

 on the rod R. Fig. 132 is a section of the condenser and water-cell. 

 The condenser is a triple system between the two anterior elements of 

 which the water-cell is placed, securing the maximum absorption of heat 

 rays with the minimum loss of light. The hand-fed electric arc lamp 

 is shown in Fig. 133 and is formed of a vertical and a horizontal carbon, 

 which are therefore at right angles to one another. They can be 

 actuated simultaneously or separately. The placing of the carbons at 

 an angle of 90° to one another with the horizontal carbon in the optical 

 axis not only throws a greater volume of light from the crater of the 

 positive carbon through the condensing lenses, but retains the glowing 

 crater always exactly in the optical axis, no matter how irregularly the 

 two carbons may burn. Fig. 134 shows the whole apparatus complete. 



