314 WRITINGS OF JOSEPH HENRY. [1855- 



when once at rest, tends to continue at rest until put in motion 

 by some extraneous force; so also the electrical fluid, when at 

 rest, tends to remain at rest, and only moves in obedience to 

 some impulse from wathout. From this theoretical inference, 

 which is in accordance with all observation it is an error to 

 suppose that electricity is an ultimate power of nature, being 

 in itself the cause of motion. Like the air, it is inert, and 

 has no more tendency to spontaneous motion than this or 

 any other fluid which may receive and transmit impulses, 

 or which may have its equilibrium disturbed, and in the res- 

 toration of this equilibrium, give rise to motion and pro- 

 duce mechanical effects. 



Perhaps some currency is given to the idea that electricity 

 is not subject to the mechanical laws which govern the actions 

 of gross matter, because it is called an " imponderable " agent, 

 and has thus assigned to it a kind of semi-spiritual char- 

 acter. The term " imponderable," though convenient, is not 

 properly applied, since it indicates a distinction which may 

 possibly not exist. If electricity is in reality a fluid, it might 

 exhibit weight, could it be so isolated and condensed as to 

 become sensible to our balances. But whatever may be its 

 nature, the phenomena which it exhibits can be referred to 

 mechanical laws; and it is in order that such a reference 

 may be definitely made, that the hypothesis of a fluid is 

 adopted. For a similar reason the phenomena of light and 

 radiant heat are referred to the vibrations of the setherial 

 medium, and it is in this way that the laws of motion which 

 have been deduced from the study of gross matter have been 

 so successfully applied to them, and it is only so far as 

 the facts of what are called the "imponderable" agents are 

 brought under the category of mechanical laws that they take 

 the definite form which entitles them to the name of science. 



Theoretical Deductions and Illustrations. — We do not intend 

 to develop from the theory we have presented a complete 

 system of electricity, but to give such deductions from it as 

 will put the intelligent reader in possession of the principal 

 known facts of atmospheric electricity, and particularly those 

 which relate to thunder storms. 



