CN HEAT AND LIGHT* 157 



To fee now by what law heat would be propagated In a folid'ff tne folld <T- 



i-ii r i r .i • i- j i • .. Under confift of 



cylinder, let us repreient the axis or this cylinder by a right three cqu j_ d ;f. 

 line A E, Plats VII. Fig. 1 ; (fee our laft nnmber) and let us taat panicles, 

 begin with fuppofing that the cylinder coniifts of three particles 

 of matter only, ACE, .placed at equal ditlances in that line. 



Let us farther fuppofe, that the extremity A of the cylinder —and the ex- 

 is conftantly at the temperature of boiling water, while its tremes at the 

 other extremity, E, remains invariably at the freezing point, freezing tera- 



By an experiment, of which I have already given an ac- peratures. 



./.»--.«- . , , iii' a. t* Then the rnid- 



count to the dais*, I found that when two equal bodies, A B, dle part i c ) e 



one hotter than the other, are ifolated and placed opposite would have the 



each other, the intensities of their radiations are fuch, that * temperature » 



third body, C, placed in the middle of the fpace that feparates A body midway 



them, will acquire a temperature by the Simultaneous aclion otherTac^ires 



of thefe radiations, which will be an arithmetical mean be- the mean heat 



tween thofe of the two bodies A and B. b ? radiation, 



From the refult of this experiment we have ground to con- «_^ r li3 o 

 elude, that if the cylinder were compofed of three particles 

 of matter only, A, C, E, the particle C, which is in the mid- 

 dle of the cylinder, mult neceflarily have the arithmetical 

 mean temperature between that of A and that of E, which 

 are at the two extremities of the cylinder; that is to fay, be- 

 tween 212° and 52° of Fahrenheit, which is 122°. 



Now let us interpofe between the particles A, C, and E, Suppofe twe 



two other particles B D, and fee whether the introduaion G f mo / e P article * 



1 y t to be interpoied, 



thefe two particles will make any change in the temperature 



of the particle C that occupies the middle of the cylinder. 



If the particle B be placed in the middle of the fpace com- Thefe woull 



prifed between the extremity A of the cylinder and its middle, cach take the 



* . J J mean temper- 



C, it ought to acquire a mean temperature between that or the a ture between 

 extremity A of the cylinder, and that of the point C, namely the middle pay- 

 that of 167°, the mean between 212* and 122°; and if the nea reft end par- 

 particle D be placed in the midft of the fpace comprifed be- tide, 

 tween the middle of the cylinder and its other extremity, E, 

 this particle ought to acquire a mean temperature between 

 that of the middle of the cylinder and that of its extremity E; 

 it ought then to have the temperature of 77°. 



From this new arrangement, the particle C, (iluate in the~" and therefore 



they would not 



middle of the cylinder, will find for its neighbours on one fide a i ter the tem- 

 perature, 



* &«e our Journal, IX. 193* 



the 



