1859] WRITINGS OP JOSEPH HENRY. 105 



recognized principle of philosophy to adopt no other causes 

 for the explanation of phenomena than are true and suf- 

 ficient; and although the existence of the setherial medium 

 may by some be doubted, yet to me it appears as certain as 

 any fact can be which rests upon inferences drawn from ob- 

 served phenomena. The wave motions which we refer to it, 

 and which exactly agree with the observed facts, are precisely 

 such as are produced in gross matter under the action of the 

 laws of force and motion, and therefore we have nearly the 

 same reason for believing in the existence of this diffused 

 substance as in that of gross matter itself. Besides, the tend- 

 ency of science is to reduce rather than increase the num- 

 ber of agencies to which effects are referred as causes. We 

 shall therefore assume that the setherial medium is also the 

 agent by which the phenomena of electricity are produced, 

 but the facts classed under the head of electricity cannot be ex- 

 plained on the principle of wave-motions, and we must 

 therefore seek for some other probable mechanical action 

 from which they may be rationally deduced. 



Electrical phenomena may be referred to two great classes, 

 statical and dynamical, or such as appear to be produced by 

 the repulsive action of a fluid at rest, and by the same fluid 

 in a state of motion. In some cases we have action at a 

 distance on surrounding bodies which develop new and per- 

 manent properties so long as the conditions remain the same ; 

 and in other cases effects which exactly resemble those of a 

 transfer — not of a property, but of actual substance, from 

 one body to the other. Now these phenomena may be re- 

 ferred to an accumulation of the setherial medium in one 

 portion of space, and a corresponding diminution in the 

 adjacent space. If the particles of the setherial medium, 

 when thus accumulated, act at a distance on other portions 

 of the same medium we shall have a rational exposition 

 of the phenomena of statical electricity; and in the restora- 

 tion of the equilibrium of the medium, or in its return 

 to its normal condition, we have a plausible cause of the 

 dynamic effects belonging to the same class. But how is 

 this disturbance of the equilibrium of the setherial me- 



