282 Mr. G. F. Rodwell on the Effect of Heat on 



The lever S bears against a second lever U, pivoted at V. From the 

 opposite extremity of U a yery fine steel chain such as is employed 



in watches, passes to a vertical axis X, which carries the needle B. The 

 needle is brought back to zero by the pressure of the spring T against 

 the lever U, and also by a fine steel mainspring Z, which is fixed to the 

 vertical axis X. a is a small pin to stop the lever U as soon as the 

 needle has passed the zero-point by a few degrees. 



The levers are shown in section in fig. 3 ; the lettering is the same 

 throughout. The framework b is of brass, as are also the levers ; the 

 pivots are of steel. Pieces of glass, c c, are let into the levers at the 

 bearing points to diminish the friction. The micrometer has threads 

 of an inch apart; hence one turn of the micrometer-head is equal to 

 of an mch, and the movement of the head through one division is 

 equal to xs"} o o" ^^^^ ' quite easy to read to half a division, 



and hence to -^^jjjy of an inch. The rods inserted between the micro- 

 meter and the lever are six inches long, and from one quarter to half an 

 inch in diameter ; they rest on light glass rollers placed in the trough F. 

 A rod of the substance to be examined is inserted between E and H; 



