FROM WOOD AND COAL. 



interchange of heat can take place between them. We may 

 consider this escape of heat, however, in the same point of 

 light as we do that which is conducted off by the surface of 

 every other part of the room, with this difference — thai this 

 particular surface of f wo inches diameter, convey* man heat in 

 a given time, than any other equal surface ; hut as this differ- 

 ence is uniform in all the experiments, we may say, compara- 

 tively, that there is no loss of heat, as it is the ratio, and nol 

 the positive quantity of heat disengaged, which we wish to 

 discover. 



2d. That the recipient body be always affected equally by the 

 communication of the same heat. 



Air has been selected as the recipient body, because we arc 

 enabled by a thermometer to measure with accuracy the heat 

 communicated to it; and because it varies very little in its 

 specific heat, under the ordinary changes of barometric pres- 

 sure, and its hygrometric changes may be readily counter- 

 acted. 



3. That the surrounding refrigerating medium be permanent 

 at any required temperature. 



In consequence of the variations in the temperature of tin 

 atmosphere, not only daily, but in different parts of the sami 

 day, to devise a plan which should strictly comply with this 

 requisition, was a subject which caused me much reflection 

 and perplexity. The room selected for my experiments, was 

 well calculated, in every respect, (except the window.) to pre- 

 vent an immediate influence being produced in its temperature, 

 by the ordinary external changes. The window being large, 

 I determined to close it entirely, and to perform my experi- 

 ments by lamp li^ht. and it was, accordingly, perfectly closed 

 on the inside of the room, with hoards, which were well 

 seasoned, and grooved together, leaving a space of four inch< - 

 between this barricade and the sashes of the window. This 

 space being occupied with confined air. was a had conductor 

 of heat. Finding it inconvenient, and objectionable in other 

 respects, to experiment with artificial light, a sash with four 

 panes of glass was subsequently inserted in this barricade, foj 



