256 WRITINGS OF JOSEPH HENRY. [1846 



under three heads, namely, the law of inertia or tendency to 

 resist a change of state and to move in a straight line with a 

 constant velocity, the law of the co-existence of separate 

 motions, and the law of the equality of action and reaction. 



The explanation of a mechanical phenomenon consists in 

 its analysis and the reference of its several parts to the fore- 

 going laws of force and motion, and as no phenomenon, 

 whether it relates to masses or the minutest portions of 

 matter is fully explained until it can be referred to one or 

 more of these laws it follows that any corpuscular hypothesis 

 which does not ascribe to each atom of matter the property 

 of obedience to the same laws must be defective. It was for 

 this reason that in printing a syllabus of his lectures about 

 two years ago he was induced to make some additions to the 

 assumptions on which the corpuscular hypothesis of Bosco- 

 vich is founded. According to this celebrated hypothesis, a 

 portion of matter consists of an assemblage in space of an 

 indefinite number of points kept at a given distance by 

 attracting and repelling forces: these points have relative 

 position but not magnitude, and are merely centers of action 

 of the forces which affect our senses, and since all our knowl- 

 edge of matter is derived from the action of these forces, 

 to infer that these points are anything more than the centers 

 of forces is going beyond our premises. 



This hypothesis readily explains the statical properties of 

 bodies, such as elasticity, porosity, impenetrability, solidity, 

 liquidity, crystallization, resistance to compression when a 

 force is applied to either side of the body, etc. ; but it fails 

 to account for the dynamic phenomena of masses of matter, 

 or those which are referable to the three laws of motion. It 

 is not therefore enough that we assume, as the elements 

 of matter, an assemblage of points in space from which 

 merely emanate attracting and repelling forces ; we must 

 also suppose these points to be endowed with inertia, or a ten- 

 dency to resist a change of state, whether of rest or motion, 

 and a tendency to move in a straight line ; also to possess 

 the property of preserving the effects of a number of im- 

 pulses, as well as that of transferring motion from one point 



