18 ON THE HEAT EVOLVED 



occurrence, no investigation of the cause was at that time 

 entered into. The trial experiment was commenced under 

 a firm belief that the differential thermometer would give- 

 immediate notice that the temperature of the exterior room 

 required correction, but, to my astonishment, the differential 

 thermometer was found to vary less than usual, and after a lapse 

 of three hours, although the temperature of the atmosphere 

 was found to have been elevated 12°, the temperature of the 

 exterior room remained stationary, and continued so until the 

 completion of the experiment. 



No time was then lost in attempting to discover the cause 

 by which an effect so desirable had been produced, and when 

 examined, it became a matter of surprise that it had not pre- 

 viously been discovered by calculation and experiment, rather 

 than accident. It may be explained in the following manner : 



The interior room contains 512, and the exterior 860 cubic 

 feet of air. As the heat necessary to elevate 512 cubic feet 

 of air 15°, is gradually transferred to 860 cubic feet, conse- 

 quently, it must increase its temperature so long as its incre- 

 ments are greater than its decrements, and should, by calcula- 

 tion, cxteris paribus, augment it nearly 9°, instead of 5°, as was 

 found to be the case ; but as the exterior room presents very 

 nearly double the conducting surface, this will account for the 

 difference. 



When the temperature of the interior room is thus elevated 

 15°, the exterior is consequently elevated 5°, by which the re- 

 quired difference of 10° is produced, and the temperature of 

 the exterior room then becomes stationary, that being the pre- 

 cise point at which the increments and decrements of heat are 

 <$jual in the air of both rooms. 



The manner of producing this important result under known 

 circumstances, being established, the operator has only to seek 

 for the same result in a different place, under an unknown, or 

 known difference of circumstances. As the surface of the 

 window (the barricade having been removed) is the only part 

 of the exterior room which can be speedily operated upon by 

 the ordinary changes of the atmosphere, the temperature of 



