222 ELEMENTS OF STATIC ELECTRICITY. 



nor the conductor, has ever received the slightest injury 

 from lightning; while numerous instances of damage 

 to buildings and conductors have occurred in the vicin- 

 ity. Which, considering the length of time, the 

 exposed position, and the repeated thunder storms of 

 great severity, which have occurred, is strong negative 

 evidence of the value of the conductor, and the correct- 

 ness of the rules here given. 



SILENT DISCHARGE. The protection afforded by a 

 lightning conductor does not consist, so much, in its 

 being the avenue by which a destructive discharge may 

 pass harmlessly between the earth and cloud ; as in 

 preventing its occurrence, by a gradual, silent discharge 

 through the points of the conductor; by which the 

 accumulated energy is reduced, before it can acquire 

 sufficient tension to overcome the resistance of the air, 

 and produce a full, sudden, disruptive discharge. 



This is strikingly illustrated by the gradual, silent 

 discharge of a large, powerfully charged Leyden bat- 

 tery, through the point of a cambric needle ; and is 

 confirmed by the brush discharge, often observed, 

 during thunder storms, on the points of lightning 

 conductors, and on the tips of the masts and yard-arms 

 of ships. 



As a building must be regarded, electrically, as an 

 elevated part of the earth's surface, the importance of 

 as perfect an electric connection between it and the 

 conductor, as practicable, is apparent, in order to 

 secure the full benefit of protection in the manner de- 

 scribed ; which is impaired by the resistance caused by 

 the use of insulators. 



It is also apparent, that the conductor affords equal 

 protection whether the discharge is from the cloud to 



