On the Coefficients of Expansion, 8fc. 541 



block, to winch the box containing the levers and the upright carrying 

 the micrometer head were firmly bolted. 



This block with figs. 1, 2, 3 is a reprint from " Proceedings," vol. 25, p. 280-282, 

 where all are described. 



2. The levers S, U (fig. 2) were reduced in weight. 



3. The spring T (fig. 2) was removed, as it was found that the 

 recoil of the helical spring Z was quite sufficient to bring the index 

 back to zero, and the presence of Y served only to increase the resist- 

 ance and general strain. 



4. The vertical axis X (figs. 1 and 3) was no longer allowed to 

 work in the upper confining plate of the framework h, but it was 

 caused to turn lightly on a bent arm above, while below it rested upon 

 a slightly hollowed ruby. 



5. The steel chain W communicating motion from the lever U to the 

 vertical axis X, which carries the index, was shortened and caused to 

 wind upon the barrel in such a manner that when unwound to the 



