106 WRITINGS OF JOSEPH HENRY. [1855- 



dium produced? The answer is, by the agency of gross 

 matter. From the refraction of light and the various effects 

 of heat we must infer that the setherial medium is intimately 

 connected with gross matter; and although the latter may 

 move in it without disturbing the equilibrium, yet when 

 two pieces of gross matter are rubbed together an accumu- 

 lation of the atoms of the aetherial medium may take place 

 on the one and a deficiency on the other. According to this 

 view there can be no electrical excitement in celestial space; 

 for there gross matter does not exist, without which the 

 medium cannot be coerced or the equilibrium disturbed. 

 It is not supposed, in accordance with this hypothesis, that 

 there is an absolute vacuum produced in the medium, but 

 that a condensation exists in a given spot, and a correspond- 

 ing rarefaction in the space around it. The degree of this 

 condensation and rarefaction ma}^ be exceedingly slight 

 in comparison with the whole elastic force of the medium, 

 and therefore it is not essential to the truth of the hypothe- 

 sis that any very perceptible changes should be produced in 

 rays of light passing in close approximation to electrified 

 bodies. 



This hypothesis is adapted to the theory of either one or 

 two fluids. In the second case the setherial medium must 

 be supposed to consist of two kinds of atoms, the separa- 

 tion of which gives rise to the phenomena observed; and 

 in the first that it consists of but one kind of atom, and 

 that the effects observed are due to its being in excess in one 

 body, and in deficiency, at the same time, in another. 



In a new investigation of the discharge of a Leyden jar, 

 by the author of this essay, the facts clearly indicated the 

 transfer of a fluid from the inside to the outside, and a re- 

 bound back and forward several times in succession, until 

 the equilibrium was attained by a series of diminishing 

 oscillations. 



The magnetic phenomena may be referred to an assem- 

 blage of electrical currents, according to the theory of Am- 

 pere, or to a peculiar arrangement of the aetherial atoms 

 within the magnetic body. 



