322 MEMORIAL OF JOSEPH HENRY. 



solid substance increases the radiation of the heat of a flame, is an 

 interesting fact in connection with the nature of heat itself. It 

 would seem to show that the vibrations of gross matter are neces- 

 sary to give sufficient intensity of impulse to produce the phe- 

 nomena of ordinary radiant heat." * 



In 1851, he read before the American Association at Albany, a 

 paper "On the Theory of the so-called Imponderables:" (mainly a 

 development of his earlier discussion in 1846, of the molecular 

 constitution of matter,) in which he forcibly criticised a frequent 

 tendency to assume or multiply unknown and unrealizable modes 

 of action : holding that with regard to the most subtle agencies of 

 nature, we have no warrant by the strict scientific method, for 

 resorting to other than the observed and established laws of matter 

 and force, until it has been exhaustively demonstrated that these 

 are insufficient. The fundamental laws of mechanical philosophy 

 "are five in number; viz. the two laws of force attraction, and 

 repulsion, varying with some function of the distance; and secondly, 

 the three laws of motion the law of inertia, of the co-existence 

 of motions, and of action and re-action. Of these laws we can 

 give no explanation : they are at present considered as ultimate 

 facts ; to which all mechanical phenomena are referred, or from 

 which they are deduced by logical inference. The existence of 

 these laws as has been said, is deduced from the phenomena of the 

 operations of matter in masses ; but we apply them by analogy to 

 the minute and invisible portions of matter which constitute the 

 atoms or molecules of gases, and we find that the inferences from 

 this assumption are borne out by the results of experience." He 

 regarded the modern kinetic or dynamic theory of gases, by its 

 predictions and verifications, as furnishing almost a complete estab- 

 lishment of the atomic and molecular theory of matter. Referring 

 to the ingenious hypothesis of Boscovich, he thought that though 

 well adapted to embrace the two static laws above mentioned, it did 

 not appear equally well adapted to satisfy in any intelligible sense 

 the three kinetic laws. He contended that any attempt at conform- 

 ing our conception of the ultimate constitution of matter to the 



* Proceed. Am. Assoc. Providence, Aug. 1855, pp. 112-116. "On the Effect of min- 

 gling Radiating substances with Combustible materials." 



