THE WEATHER. 227 



principles explaining them, have been thoroughly inves- 

 tigated ; but others baffle all human efforts. 



There is a certain something, called by philosophers 

 electric fluid, which is diffused naturally over all bodies. 

 It is in the chair in which I sit, in the table, the paper, 

 my hand, in a word, in everything. In its natural 

 state it is equally and generally diffused and produces no 

 sensible effects. But there are certain causes which colled 

 it. When it is thus accumulated in one place .or upon 

 one body, it produces very striking results : one of the 

 most remarkable of which is, it tends to dart away into 

 the surrounding objects, with a bright spark and a noise. 

 This can be easily imitated on a small scale with the 

 electrical machine ; and it is this agent, operating pre- 

 cisely in this way, but with tremendous energy and 

 splendor, which so often terrifies us in the skies. 



Among the processes by which the electric fluid is 

 accumulated, and thus prepared to produce these sensible 

 effects, one of the principal is, the condensation of vapor, 

 as described on a preceding page. This is shown by a 

 simple electrical experiment which it is not necessary to 

 describe particularly here. But it is considered as estab- 

 lished, that whenever the vapor of the atmosphere is 

 condensed, electricity is collected, and tends to dart off 

 into surrounding objects. Whenever a cloud is formed 

 in the sky it probably becomes more or less charged with 

 electricity. 



Now it is one remarkable property of this electric fluid, 

 that some substances easily convey it away and others do 

 not. The former are called Conductors, the latter Non- 

 Conductors. The metals and water are the conductors : 

 almost all other substances, non-conductors. 



Whenever the electric fluid is collected in any place, 

 if there is a conductor, or a chain of conductors, to 

 convey it away, it passes off silently and without any 

 sensible effect. If there are no conductors, it accumu- 

 lates until it becomes excessive in quantity, and then it 

 darts off through the air or any substances which are in 

 its way, sometimes with great violence and often doing 

 irreparable injury. 



We do not, however, always have thunder and lightning 

 when clouds form in : the sky. When a fog rolls in from 



