218 ELEMENTS OF STATIC ELECTRICITY. 



as to the space protected by a conductor ; as opinion 

 and practice vary in regard to it: but there is no well 

 authenticated instance of a building furnished with a 

 property constructed conductor, having been injured 

 by lightning within a conical space, having the point 

 of the upper terminal for its apex, and the radius of 

 whose base equaled the height of the conductor. 



ATTACHMENT TO BUILDING. The evidence against 

 the use of glass or other material, in order to insulate 

 the conductor, is overwhelming ; and insulation may 

 be regarded as unnecessary and mischievous. The. 

 attachment to the building should be made with metal 

 fastenings ; which should be of the same metal as the 

 conductor itself, to prevent corrosion from galvanic 

 action. They should be of adequate strength : and 

 each should support its proper proportion of the weight. 

 They should not compress or distort the conductor; and 

 should allow free play for its expansion and contraction. 



As far as practicable, it is desirable that conductors 

 be connected with extensive masses of metal belonging 

 to the building, both internal and external; except 

 soft metal pipes, which, from low conductivity for heat 

 and electricity, are liable to fusion. Gas-pipes, es- 

 pecially, should not be so connected on account of 

 liability to ignition of the gas by an electric spark, 

 resulting from fusion of the pipe, or from bad joints : 

 but the inlet and outlet pipes of large gas meters should 

 always be electrically connected with each other, as a 

 protection against such accidents from the electric 

 resistance of joints; which is sometimes greatly in- 

 creased by india-rubber packing. 



Church bells, inside well protected steeples, need 

 not be connected with the conductor. 



