A SYSTEM OF PARTICLES. 277 



I cannot, however, admit such an objection, as the great difficulty 

 which hangs about absorption is its elective character, which is not 

 at all necessary, as far as we know, for Heat. 



44. But allowing all the difficulties, it is desirable to adopt an 

 hypothesis which has some chance of meeting a few of them, and 

 I hope it is not quite unimportant to shew that if the vibration in 

 one plane be stopped (as for instance if ^ = 0), the transmission is 

 affected by a constant loss, and if another substance be so placed, 

 that the corresponding planes in the two are parallel, c" will not be 

 destroyed by it, whilst on the other hand, if they are perpendicular, 

 it will ; which is, in fact, such an explanation as will account for 

 the phenomena. 



It appeared to me utterly impossible to refer the phenomena of 

 Heat to vibrations in the same manner as we do those of light, from 

 the obvious circumstance that a new and permanent /orce seems 

 necessary in the consideration, and this must plead my apology for 

 bringing these speculations before the Society. 



45. I would have it observed that although in the majority of cases 

 I have spoken as though I consider one attractive medium (at least 

 as far as the action of the particles on each other is concerned,) 

 sufficient to account for the phenomena, it is not at all my wish to 

 have it supposed that I am anxious to advocate such an hypothesis. 

 If we choose rather, in the present state of our knowledge of the 

 subject, to admit Coulomb's hypothesis of two media, whose particles, 

 respectively, act repulsively on particles of the same medium, and 

 attractively on those of the other, none of my conclusions will be in 

 the slightest degree affected, provided we allow that the effects of 

 vibration, and transfer of which we have been speaking, have refer- 



ence to the medium A, for which the quantity - — + ^ is positive, 

 or -75^ > — J- , so that the mutual action of two consecutive particles of 



6 6 



the moving media is less than that of the other. 



N N 2 



