18 On tJie ConstiUdion of Matter, 



which vanishes for all values of s, except s ^ v, and in that case 

 a n 



IS 



2 cos V y 



o-'r = a cos (2 r — 1) 'Z^ y cos jctv t 



|u,v = 2 m sin v y = 2 m sin vj/ = jw, 



cos (2 r — 1) vl/ , 



a^j. = a b l_L cos jU. ^ 



cos rj/ 



or the motion continues, in this case, to be the same exactly as 

 that impressed upon the system by the disturbance. The system 

 in cooling would radiate the same kind of heat as that which it 

 received ; that is, it would give back the fundamental note of its 

 molecules quite pure. 



If it shall hereafter appear that we are justified in inferring 

 that atoms under any natural arrangement, under the action of 

 heat of a certain wave length, would behave in a manner 

 analogous to that which they appear to adopt when constrained to 

 move in a straight line, then I think it will be found that 

 we have fiUen upon a principle of great importance in the 

 economy of nature. It may be briefly stated thus. The arrange- 

 ment of atoms in a molecule is caused by the prevalent heat, and 

 depends upon its wave length ; and every molecule generated 

 under the action of heat of a certain wave length, radiates heat 

 of the same, or nearly the same, wave length. I do not consider 

 of course, that the existence of this principle is proved, or that 

 these investigations aff'ord us anything more perhaps, than a hint 

 of the truth. In the further remarks which I shall have to make, 



1 shall however assume the truth of the principle which I have 

 stated ; but I hope that it will be understood, if I appear to 

 adopt too confident a tone, that I do so merely to avoid the 

 awkward recurrence of a hypothetical mode of expression. 



Before indulging in any speculations, I must dwell a little 

 longer upon the dry forms. We will endeavour to form some general 

 idea of the value of vf/ from the equations [x. = 2 m sin \{/, 



2 p ^ = 77. ft, we know, is very large, andw for ordinary solids 

 must also be very large, for the molecular forces are enormous in 



relation to the masses upon which they act. If \|/ ^ -, then 



p = 2; if \J/ is greater than -, ^ = 1, or the supposed molecular 

 arrangement would not occur. If there be any simple substance 

 for which vj; is greater than - it must exist in the state of in- 

 dependent atoms and be incapable of assuming the liquid state, 



