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of force and motion, we are obliged to assume the existence of an 

 ethereal medium formed of atoms, which are endowed with precisely 

 the same properties as those we have assigned to common matter ; 

 and this assumption leads us to the inference, that matter is diffused 

 through all space. 



That something exists between us and the sun, possessing the pro- 

 perties 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 mecha- 

 nical properties we have mentioned. Indeed, the motion is analo- 

 gous, though not precisely similar to the transmission of sound 

 through air; the time, however, in the two cases, being very dif- 

 ferent. Light passes the space between us and the sun in about eight 

 minutes, while sound, through air, would require 13| years to per- 

 form the same journey. This difference in velocity is, however, 

 readily explained by a difference in density and elasticity of air, and 

 the ethereal medium. That the phenomena of light and heat from 

 the sun are not the effect of transmission, without intervening matter, 

 of mere force, such as that of attraction or repulsion, is evident from 

 the fact, that these actions require no perceptible time for their trans- 

 mission to the most distant part of the solar system. If the sun were 

 at once to be annihilated, the planet Neptune would, at the same in- 

 stant, begin to move in a tangent to its present orbit. Also, the phe- 

 nomena of electricity and magnetism involve the consideration of 

 time; the discharge of the former through a copper wire is trans- 

 mitted with about the velocity of light, and the development of the 

 latter, in an iron bar, is attended with a change in the ponderable 

 molecules of the metal, which requires time for its completion. 



According to the foregoing views we may assume, with Newton, 

 the existence of one kind of matter diffused throughout all space, and 

 existing in four states, namely, the ethereal, the aeriform, the liquid, 

 and the solid. This method of presenting the atomic hypothesis of 

 the constitution of matter, may at first sight appear startling; but on 

 a little reflection, it will be found a necessary consequence of the 

 attempt to explain the mechanical phenomena of matter by an as- 

 semblage of separate atoms. It may be objected to the assumption 

 of one kind of matter, that the fact of the imponderable nature of 

 light, heat, electricity and magnetism, require at least two kinds of 

 matter; but if we adopt the theory of undulation, the phenomena of 



