and the effects of lightning on HM.S. Rodney ^ 121 
concerning the precise nature of electricity, yet the following 
explanation runs sufficiently parallel with facts to entitle it to 
our confidence, and put us in possession of one of the great 
advantages of every theory, viz. a classification and connexion 
of observed effects ; the province of human knowledge, being, 
as justly observed by a most intellectual and accomplished 
writer^ ^‘to observe facts, and trace what their relations 
are*’’ 
General principles : — 
10. There is an invisible agency in the material world inti- 
mately associated with common matter, termed electricity. 
11. Lightning, thunder, and a variety of analogous phaeno- 
mena of a minor kind, artificially produced, result from dis- 
charges of this agency between bodies differently affected 
by it. 
12. In every case of electrical discharge there are two 
surfaces of action ; one existing on some substance eager to 
throw off’ redundant electricity, being, according to Dr. Frank- 
lin, overcharged with it ; the other existing in some other sub- 
stance eager to receive electricity, being, according to the same 
philosopher, deficient of it, or undercharged. 
13. Two opposed bodies, when placed in these opposite 
electrical states, have, a sort of exclusive action on each other, 
either directly through any intervening substance, whether a 
conductor of the electrical principle or not, or otherwise indi- 
rectly through any lateral circuit. 
Thus two metallic surfaces A B (fig. 1.) pasted on the op- 
posite sides of a square of glass c have, when the square 
is said to be charged, an exclusive action on each other, either 
through the intervening glass, or otherwise through any con- 
ductor, A o B, connecting them. 
Now we have only to suppose these planes placed further 
apart, as in fig. 2, to have a discharging conductor, m ??, of 
greater or less extent between them, to be greatly increased in 
size, to be separated by air instead of glass, and to consist of 
free vapour or water, and we have a pretty faithful repre- 
sentation of the conditions, under which a discharge of light- 
ning takes place, when passing partly through the air, and 
partly through a discharging conductor, m w, or any other 
body, c d, placed on the plane Bf. 
* Abercrombie on the Intellectual Powers. 
t The thickness of the intervening air, and the amount of free elec- 
tricity in the clouds, has led Professor Henry to question in some measure, 
the perfect analogy of a discharge of lightning, with that of a Leyden jar ; 
but I think upon mature consideration this circumstance will not be found 
in any way subversive of the general principle. Thus whether electricity 
