Thermotic Effect of Compression and Expansion of Air, 115 



tion of the piston, and conduction and radiation by the pipes, 

 -^first, the increase of heat which air undergoes when sub- 

 mitted to a compressing force of 3 lb. per square inch ; and 

 second, the decrease of heat on escaping from the same. 



The air is carried by four short wide tubes immediately 

 from the pumps, — which are enclosed in the engine-house, and 

 lie horizontally, — to a large sheet-iron tubular reservoir, con- 

 tained between, the roof and the ceiling of the said house ; 

 and thence by long pipes to the several funiaces. There is 

 nothing beyond the elasticity of the air itself to equalize the 

 pressure during the different parts of the stroke of the pump ; 

 and the particular exertion of 3 lb. being only the consequence 

 of the quantity of air forced in by the pumps, and the area of 

 exit hole in the furnaces, — is liable to alter continually, as one 

 or another furnace may be turned off or put on again from 

 time to time. 



Having proceeded to the place in company with Mr Stir- 

 ling, C. E., and Captain Driscoll Gosset, R. E., in December 

 29, 1849, we determined to operate on the large reservoir in 

 the enclosed space between the ceiling androof of the engine- 

 house ; and Mr Wilson's men having obligingly bored a hole 

 in the flat end of the reservoir, we thrust therein a tin tube 

 armed with stopcocks, thermometers, and a mercurial pres- 

 sure-gauge. 



Reservoir qjf 



confessed 



air 



The tube was made in two halves, so that the first, pro- 

 vided only with a stopcock, might have its conical end forci- 

 bly driven into the hole, and, when fairly fastened there, the 

 other half was connected by a union joint. The first stop- 

 cock being now open, the compressed air of the reservoir, 

 which had hitherto reached so far, proceeded on into the 

 second tube which had another stopcock near its extremity. 



h2 



