Art. X. — On Lightning Conductors. 

 By Phofessor Kernot. 



[Read 12th August, 1886.] 



A PROPERLY constructed lightning-conductor acts in two 

 different ways. 



1st. It gradually and silently draws the electricity away 

 from the clouds in the same way as a pointed wire in com- 

 munication with the earth draws, or, as it is sometimes 

 expressed, sucks the electricity away from the charged con- 

 ductor of an ordinary frictional electrical machine. Every 

 conductor that acts in this way is a public benefit, mitigat- 

 ing the severity of thunderstorms in the locality where it 

 is situated. Hence it would be a perfectly reasonable and 

 proper thing to erect conductors at the public expense upon 

 all lofty buildings or other elevated points in the vicinity of 

 a town. The effect of a single conductor would probably 

 be imperceptible, or nearly so, in this respect ; but the effect 

 of a score or a hundred would be manifest in a marked 

 diminution in the intensity of atmospheric electric 

 phenomena over or to the leeward of the place where they 

 were situated. In order to be efficient for this purpose a 

 conductor should— first, be provided with one or more fine, 

 sharp points at its upper termination; second, have its own 

 electric resistance small ; third, have a good earth connection. 



2nd. When the building is actually struck by lightning, the 

 conductor may be of great use by attracting the discharge 

 to itself and away from other parts of the structure, and 

 conveying it harmlessly to the earth. For this purpose it 

 should — first, be so prominent as to necessarily receive th^ 

 electric spark, no matter from what direction the electrified 

 cloud travels; second, be of such sectional area as to convey 

 the largest discharge likely to occur without being heated to 

 such an extent as to fuse or become distorted; third, have 

 its own resistance and that of its earth connection distinctly 

 smaller than that of any water-pipe, gas-pipe, or other con- 

 ducting mass in its vicinity. 



In addition to the above, it is a wise precaution to connect 

 the conductor with all the principal metallic masses in the 



