Lightning Conductors in Ships. 349 
conducting or insulating power of some substances, compared with 
that of others, may be considered as imperfect: hence has arisen a 
third class, which consists of the remote extremes of the other two, 
and which may be considered in the power of arresting or transmit- 
ting certain electrical actions as appertaining to either. Thus wood, 
hemp, stone, and the like, may become insulators to a state of low 
electrical action, and conductors to a high one. 
- The manner in which accumulations of atmospheric electricity 
proceed, may be referred to the following principle: When two sub- 
stances of the conducting class are directly opposed to each other, 
and are separated by a substance of the non-conducting or insulating 
class, leaving the one free and the other insulated, the proportionate 
state of electrical distribution may become deranged to the greatest 
Possible extent. Now, in nature, the conditions of such an experi- 
ment are found in the relative situations of the sea and clouds, and 
intervening air; so that when, from any cause, an evolution of natu- 
ral electricity takes place, and heavy masses of vapor are present in 
the atmosphere, we have immediately an insulated conductor, (a 
cloud,) directly opposed to a conductor in a free state (the sea or 
land,) and an intervening non-conducting or insulating medium, the 
air; hence results a charged battery of enormous power : the attrac- 
tion of the opposite electrical states, therefore, may become at length 
*0 powerful, that the electric matter breaks down the intervening re- 
sisting air, with a terrific and dense explosion—an effect perfectly 
analogous to the explosion which frequently occurs at the time of 
‘onveying a high charge to an electrical battery, and which is attend- 
ed by a peculiar fracture of the interposed glass. 
- The year 1752, which marks an important era in electrical sci~ 
face, from the celebrated discovery of the principle just mentioned, 
under the form of the Leyden jar, gave to the natural philosopher an 
®asy method of concentrating large quantities of electricity produced 
by artificial means, so as to discharge it upon or through bodies with 
%n instantaneous and violent explosion. From the time, therefore, 
at the cause of lightning became identified with that of ordinary 
clectricity, and that the gigantic attempt of Dr. Franklin and other 
P ilosophers, of actually drawing down the matter of lightning from 
si An explanation of some of the phenomena of thunder-storms on this principle 
Will be found in my printed letter to Sir T. B. Martin, K.C.B. Comptroller of his 
Majesty's Navy, 
