116 MR. H. WILDE ON THE INFLUENCE OF GAS- AND 



In my experiments on the electrical condition of the 

 terrestrial globe, I have already directed attention to the 

 powerful influence which lines of metal, extended in contact 

 with moist ground, exercise in promoting the discharge of 

 electric currents of comparatively low tension into the 

 eartVs substance, and also that the amount of the 

 discharge from an electromotor into the earth increases 

 conjointly with the tension of the current and the length 

 of the conductor extended in contact with the earth. It is 

 not, therefore, surprising that atmospheric electricity, of 

 a tension sufficient to strike through a stratum of air 

 several hundred yards thick, should find an easier path to 

 the earth by leaping from a lightning-conductor through a 

 few feet of air or stone to a great system of gas- and water- 

 mains, extending in large towns for miles, than by the 

 short line of metal extended in the ground which forms the 

 usual termination of a lightning-conductor. 



It deserves to be noticed that in the cases of lightning 

 discharge which I have cited, the lightning-conductors 

 acted efficiently in protecting the buildings from damage 

 of a mechanical nature, the trifling injury to the church 

 tower at Kersal Moor being directly attributable to the 

 presence of the gas-pipe in proximity to the conductor. 

 Nor would there have been any danger from fire by the 

 ignition of the gas if all the pipes used in the interior of 

 the buildings had been made of iron or brass instead of 

 lead ; for all the cases of the ignition of gas by lightning 

 which have come under my observation have been brought 

 about by the fusion of lead pipes in the line of discharge. 

 The substitution of brass and iron, wherever lead is used 

 in the construction of gas-apparatus, would, however, be 

 attended with great inconvenience and expense, and more- 

 over would not avert other dangers incident to the 

 disruptive discharge from the conductor to the gas- and 



