52 ' BOARD OF AGRICULTURE. 



The posts supporting 1 telegraph wires are not unfrequently 

 struck by lightning — sometimes several posts in succession, and 

 sometimes between the posts struck are intermediate posts un- 

 injured. A position near telegraph posts during a thunder storm 

 is not regarded desirable. It should not be forgotten that when 

 lightning strikes men or animals ranged in a line, straight or 

 curved, those at the extremities suffer most from the stroke. 

 Bell ringers during a thunder storm occupy an unsafe place. 

 Lightning is attracted somewhat to assemblies in consequence of 

 the ascentional currents of warm, moist air, which serve as con- 

 ductors of the electric fluid. 



By what method may buildings and vessels be successfully pro- 

 tected from lightning ? In ancient times it was thought a dwelling 

 could be protected by surrounding it with white grape vines. 

 Artazerxes planted swords in the ground point uppermost, to 

 drive away clouds, hail and thunder storms. The building of 

 large fires, the discharging of cannon, and the ringing of church 

 bells, have been at different times among the means designed to 

 protect towns and even extensive districts from the falling of 

 thunderbolts. 



A more rational method then any of these, is that devised by 

 Franklin. The facts already submitted in this paper suggest the 

 method which Franklin adopted, and point irresistably to the con- 

 clusions which he reached. 



It has been shown that other circumstances being equal, light- 

 ning directs itself by preference to the most elevated portions of 

 edifices, hence there the means of protection should be applied. 

 It has been shown that other circumstances being equal, lightning 

 directs itself by preference to metallic bodies. A metallic mass, 

 therefore, placed at the most elevated part of a building, will be 

 likely to receive the electric discharge rather than the building 

 itself. It has been shown that when lightning falls upon a metallic 

 mass it does damage to surrounding bodies, at the moment of 

 quitting the metal, and in proximity to the point or points at 

 which it escapes from it. This indicates the necessity of metallic 

 continuity until some surface or receptacle is reached which may 

 safely receive the electric discharge. Damp earth offers a chan- 

 nel by which lightning may escape from a metallic rod without 

 producing damage of any kind. And thus we have the modern 

 lightning conductor devised. 



It is a curious and interesting fact that the Temple at Jerusalem, 



