1851] WRITINGS OF JOSEPH HENRY. 297 



ON THE THEORY OF THE SO-CALLED IMPONDERABLES. 



(Proceedings American Association Adv. of Science, vol. vi, pp. 84-91.) 

 August 21, 1851. 



Professor Henry said: In studying the phenomena of 

 matter we commence with observing the action of masses 

 upon each other, and from this we deduce laws. These, with 

 regard to 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, viz., the law ofinertia, 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 phe- 

 nomena 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. 



Indeed, the minutest portions of matter must be endowed 

 with properties analogous to masses of the same kind of 

 matter. An attempt has however been made by Boscovich 

 to refer all the mechanical properties of matter to portions 

 of space, filled with associated points, endowed with attract- 

 ing and repelling forces, varying and alternating with changes 

 of distances. In a communication to the American Philo- 

 sophical Society,* I have shown that this hypothesis, which 

 is at the present time adopted by many, is insufficient to 

 explain all the facts. Matter thus constituted would indeed 

 exhibit the phenomena of elasticity, compressibility, porosity, 

 affinity, etc.; but it would not exhibit an obedience to the 

 three laws of motion, namely, inertia, the co-existence or 

 composition of motions, and action and re-action. We must 



* [November G, 1846. See ante, p. 255.] 



