SCIENCE 



NEW YORK, MAY 8, 1891. 



SOME POSSIBLE MODIFICATIONS IN THE METHODS 

 OF PROTECTING BUILDINGS FROM LIGHT- 

 NING.' 



I REMEMBER with what hesitation I ventured some months 

 ago to explain to your fellow-member, Mr. T. C. Martin, my 

 ideas on some possible modifications in the method of pro- 

 tecting buildings from lightning. But as he was kind 

 enough to express the belief that there was something in 

 what I had to say, I have ventured to come here this even- 

 ing to explain my ideas to what must be an extremely criti- 

 cal audience. 



To begin with, I have always belonged with, those who 

 have been sceptical as to the utility of lightning-rods as or- 

 dinarily placed on our houses. I was never able to under- 

 stand, and cannot now, why, if a lightning-rod as ordinarily 

 introduced was useful, the lightning should scent out a bad 

 earth connection at so considerable a distance. I mean that I 

 could understand the ordinary theory of the rod if invaria- 

 bly the electrical discharge followed the rod as far as its 

 conductivity was good, only to leave it when the bad earth 

 connection was reached. 



I am aware that tlie advocates of the old form of rod point 

 to the apparent beneficial effects of the Harris system as in- 

 troduced on ships. This may be due to the possibility of 

 making an especially good earth connection, or it may be 

 due to there having been introduced on ships about the time 

 that rods were introduced some other modification which has 

 had a beneficial effect. I have some suspicions on this 

 point, and find it recorded in the London Electrical Review 

 that lightning does not play as destructive a part as it did 

 forty or' fiftf years ago, and that even those ships unprovided 

 with conductors have suffered less damage than a smaller 

 . number of ships experienced formerly. Not that modern 

 vessels are exempt, but they seem to be struck in a manner 

 which causes fewer fatal accidents, and in some cases even 

 the effects of a lightning-flash have borne so little trace of 

 their origin that they have been credited to the wilful act of 

 some one on board. 



Ordinarily a lightning-rod is regarded as a conduit or pipe 

 for conveying electricity from a cloud to the ground. The 

 idea is that a certain quantity of electricity has to get to the 

 ground somehow; that if an easy channel is opened for it, 

 the electricity will pass quietly and safely ; but that if ob- 

 struction is introduced, violence and damage will result. 

 This being the notion of what is required, a stout copper rod, 

 a wide-branching and deep-reaching system of roots to dis- 

 perse the charge as fast as the rod brings it down, and a 

 supplement of sharp points at a good elevation to tempt the 

 discharge into this attractive thoroughfare, are naturally 

 guaranties of complete security. 



I think Oliver J. Lodge has expressed well the difficulty 

 that has always been present in my mind when I have read 

 detailed descriptions of the effects of lightning. He says, in 



^ A paper, by N. D. C. Hodges, read at the fifty-sixth meeting of the Ameri- 

 can Institute of Electrical Engineers, New York, April 21. 



a paper published in the Electrical Engineer some time last 

 June, that when, in spite of all precautions, accidents still oc- 

 curred ; when it was found that from the best- constructed con- 

 ductors flashes were apt to spit off in a senseless manner to gun- 

 barrels and bell-ropes, and wire fences and water-butts, — it 

 was the custom to more or less ridicule and condemn either 

 the proprietor or its erector, or both, and to hint that if only 

 something different had been done, — say, for instance, if 

 glass insulators had not been used, or if the rod had not been 

 stapled too tightly into the wall, or if the rope had not been 

 made of stranded wires, or if copper had been used instead 

 of iron, or if the finials had been more sharply pointed, or if 

 the earth plate had been more deeply buried, or if the rain- 

 fall had not been so small, or if the testing of the conductor 

 for resistance had been more recent, or if the wall to which 

 the rod was fixed had been kept wet, — then the damage 

 would not have happened. Every one of these excuses has 

 been appealed to as an explanation of a failure; but because 

 the easiest thing to abuse has always been the buried earth 

 connection, that has come in for the most frequent blame^ 

 and has been held responsible for every accident not other- 

 wise explicable. 



I have to say, therefore, that up to about two years ago I 

 was simply in the dark as to what was the matter with 

 lightning-rods. I could not accept the reasoning set forth in 

 the report of the Lightning-Rod Conference or in any of our 

 books. It did not seem to me that the arguments in sup- 

 port of the ordinary lightning-rod were logical. It seemed 

 to me that there was something that we did not understand. 



About two years ago one of the oil-tanks at Communipaw 

 or Bayonne, just off the New Jersey Central Railroad, was 

 struck by lightning; and, as I pass that way each day, my 

 attention was again called to the question how we should 

 protect our buildings from lightning; and one evening, 

 taking up Silvaaus P. Thompson's little book on electricity, 

 I think it was, to see what he had to say about lightning, I 

 re-read the ordinary theory of the formation of the high po- 

 tentials that are manifested in lightning-discharges. 



This theory is simply this: that if, in the cloud, there 

 is a certain quantity of electricity distributed on a given 

 mass of fine mist, it will exist there at a certain potential, 

 depending on the capacity of this finely divided matter. 

 Now, if these mist-particles coalesce into raindrops, the the- 

 ory points out that there would be a decrease in the electri- 

 cal capacity, and a consequent increase in the potential of 

 the charge. It occurred to me immediately, that, if this 

 theory had any foundation in fact, it ought to be possible to 

 reverse the operation on the surface of the earth ; that is, to 

 receive the lightning discharge on some large body, which 

 would then be broken up into fine particles of vapor, which 

 would have a considerably greater electrical capacity, and 

 that the potential of the discharge would thereby be materi- 

 ally reduced, and the effects of the lightning mitigated. 

 This was my hypothesis to work upon, and I immediately 

 began to look through the records to see what actually hap- 

 pened in the case of lightning-discharges, and to see if there 

 was any support in fact for my hypothesis. 



The first book at hand was Sir William Thomson's "Pa- 



