1846] WRITINGS OF JOSEPH HENRY. 257 



to another, the one losing as much motion as the other gains. 

 But the admission of the existence of points with such qual- 

 ities brings us back to the Newtonian hypothesis of matter. 



According to the view we have given, a portion of matter 

 consists of an assemblage of indivisible and indestructible 

 atoms endowed with attracting and repelling forces, and 

 with the property of obedience to the three laws of motion. 

 All the other properties, and indeed all the mechanical phe- 

 nomena of matter, so far as they have been analyzed, are 

 probably referable to the action of such atoms, arranged in 

 groups of different orders, namely, of ultimate atoms, chem- 

 ical atoms, simple molecules, compound molecules, particles, 

 etc. ; the distance in all cases between any two atoms being 

 much greater than the diameter of the atoms or molecules. 



In order that we may bring all the phenomena of the " im- 

 ponderable" agents of nature, (as they are called,) under the 

 category of the laws of force and motion, we are obliged to 

 assume the existence of an setherial medium formed of atoms, 

 which are endowed with precisely the same properties as 

 those we have assigned to common matter ; and this assump- 

 tion leads us to the inference, that matter is diffused through 

 all space. 



That something exists between us and the sun, possessing 

 the properties of matter, may be inferred from the simple 

 fact that time is required for the transmission of light and 

 heat through the intervening space. The phenomena of the 

 transmitted motion, in these cases, are perfectly represented 

 by undulations, in a medium composed of very minute atoms 

 of ordinary matter, endowed with all the mechanical prop- 

 erties we have mentioned. Indeed, the motion is analogous — 

 though not precisely similar — to the transmission of sound 

 through air ; the time however in the two cases being very 

 different. Light passes the space between us and the sun in 

 about eight minutes, while sound (through air) would require 

 13f years to perform the same journey. This difference in 

 velocity is however readily explained by a difference in den- 

 sit}' and elasticity of air, and the eetherial medium. That 

 the phenomena of light and heat from the sun are not the 

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