HEAT OR CALORIC. 



47 



Influence of temperature on the 

 length of a metallic wire acting 

 on an index through intervening 

 levers. 



W W represents a wire, beneath 

 which is a spirit lamp, consisting of 

 a long, narrow, hollow triangular 

 vessel of sheet copper, open along 

 the upper angle, so as to receive 

 and support a strip of thick cotton 

 cloth, or a succession of wicks. 

 By the action of the screw at S, 

 the wire is tightened ; and by its 

 influence on the levers, the index 

 I is raised. The spirit lamp is 

 then lighted, and the wire is en- 

 veloped with flame. It is of course 

 heated and expanded ; and, allow- 

 ing more liberty to the levers, the 

 index, upheld by them, falls. 



By the action of the screw the 

 wire may be again tightened, and 

 the application of the lamp being 

 continued, will again, by a further 

 expansion, cause the depression of 

 the index ; so that the experiment 

 may be repeated several times in 

 succession. 



Since this figure was drawn, I 

 have substituted for the alcohol 

 lamp, the more manageable flame 

 of hydrogen gas, emitted from a 

 row of apertures in a pipe supplied 

 by a self-regulating reservoir of 

 hydrogen gas, of which an engra- 

 ving and description will be given 

 in due time. 



If while the index is depressed, 

 by the expansion, ice or cold 

 water be applied to the wire, a 

 contraction immediately follows, 

 so as to raise the index to its ori- 

 ginal position. Dr. Hare. 



