SCIENCE 



NEW YORK, MAY 15, 1891. 



SOME POSSIBLE MODIFICATIONS IN THE METHODS 

 OF PROTECTING BUILDINGS FROM LIGHT- 

 NING. — DISCUSSION. > 



[Continued from p. 255] 



Me. Edward P. Thompson: — I have listened with a great 

 deal of interest to the matter presented in the paper just 

 read. The alleged facts seem to agree with our ideas of 

 electricity of low potential. Electricity occurs ia thunder- 

 storms, and the best thing to do is to get rid of it. One way 

 is by conducting it away sufficiently rapidly by means of a 

 conductor of very large surface capacity, as the conductivity 

 of a metal as to static electricity depends upon the surface 

 and not upon the sectional area. This principle is applied 

 in the ordinary lightning-rod. As I understand the speaker, 

 he proposes to provide a system whereby the electrical en- 

 ergy is not conducted away, but converted into heat. In 

 view of the conduction principle having so often proved a 

 failure, and the conversion principle having succeeded every 

 time, according to the researches of the speaker, and since 

 his theory agrees with well-known electrical principles, I 

 think Mr. Hodges has presented matter well worthy of the 

 consideration of the institute, and I, for one, can find no ob- 

 jection to his system as to correctness of principle. As to 

 practical equipment, some incombustible non-conductor, such 

 as asbestos, should be placed between the thin metallic strip 

 and the structure to be protected, or else the melted metal 

 may set fire to the building. 



Dr. William E. Geyer: — It seems to me that the occur- 

 rence quoted here from Franklin tends to show that the 

 ordinary theory of the lightning-rod is essentially true. 

 The bell-wire, so far as it went in the occurrence here de- 

 scribed, was a lightning-rod, and protected the building so 

 far as that lightning-rod went. It was not heavy enough to 

 carry the current, and it was for that reason dissipated, so 

 that the dissipation was simply an accident. The mere dis- 

 sipation, however, did not save that part of the building 

 where the wire stopped and there was no good conductor: 

 the building was without any lightning-rod, and was more 

 damaged than where it had even a small rod. 



Mr. Townsend Wolcott: — Professor Lodge's theory of the 

 Leyden-jar discharge is that it is oscillatory under ordinary 

 conditions, that is, where the coatings are connected with a 

 good conductor. Now, if they are connected with a bad 

 conductor, such as a wet string, Professor Lodge says that 

 the discharge may be only in one direction, that is, the 

 energy is all dissipated in a single discharge ; whereas, if the 

 conductor is good, there is little energy dissipated in getting 

 from one coating to another. So far, Mr. Hodges' theory 

 would seem to agr'='e with Professor Lodge's, that if you can 

 use up the energy of the electricity in destroying the con- 

 ductor you will get rid of it more quickly than you would 

 in any other way, and the lightning will have less effect 

 outside of that. But there are some other points. Mr. 



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

 can Institute o( Electrical Engineers, New York, April 21. 



Hodges says we do not attempt to make a good connection 

 at the top with the dielectric. I do not exactly understand 

 that. We do attempt to give it good connection with a con- 

 ductor. If a cloud is charged, that is a charged conductor, 

 and so long as the current is to come down to the earth, we 

 try to get as good connection with it as we can, by putting 

 points on the lightning-rod, for instance. A better way to 

 do that would be to have a flame or something of that sort. 

 As an experiment in drawing electricity from the air, a fiame 

 is better than a point. But, of course, it would not work in 

 a thunder-storm. 



As to the point which Dr. Geyer just mentioned, that Mr. 

 Hodges' experiments support the ordinary theory of the 

 lightning-rod, I think his reasoning does, to some extent, too, 

 in regard to getting rid of the energy on the central core. 

 Take the ordinary lightning-rod. The way it is intended to 

 work is rather to prevent a disruptive discharge than it is to 

 take care of one that has already occurred. We desire to 

 equalize the difference of potential by drawing ofi' the charge 

 from the cloud before it gets to a dangerous limit. If we 

 can do that, we do not have any disruptive discharge at all. 

 It is just like a brush discharge, such as you get from a con- 

 ductor with points on an electric machine. I think the fact 

 is not questioned that lightning sometimes is discharged in 

 that way, but not always. There is the trouble. I do not 

 think that any one system of lightning-rods has proved suc- 

 cessful. Sometimes a lightning-rod will take care of several 

 discharges in a single storm, and that seems to be something 

 which Mr. Hodges' lightning-rod would not do; because, 

 after it had been dissipated by one discharge, I do not think, 

 even if it could be put up in a few moments, that anybody 

 would care to be monkeying around a conductor when there 

 was lightning. Mr. Hodges, having asked us to clear our 

 minds of the idea of conducting electricity, seems to go fur- 

 ther than most of the modern theorists on electricity. I 

 think Mr. Hodges, even if he does not use the idea of elec- 

 tricity, will admit that we want to make a metallic way en- 

 tirely down to the earth. The case is somewhat analogous 

 to the Leyden jar; that is, two conductors separated by a 

 dielectric. Now, we want to bridge over the whole space of 

 the dielectric, whether you use the idea of conductivity or 

 not. So I don't think it makes much difference whether 

 you use his dissipatable lightning-rod or a stout one. 



Mr. Hodges : — I would like to bring the discussion back 

 once more. In order to make the paper of some length, I 

 gave some theory ; but the fact as I have found it is this : I 

 know how the books state that the ship " Jupiter " was saved 

 from destruction in spite of her lightning-rod going to pieces. 

 But take the fact without going to the books at all. What 

 do the records show? I want to get a case where the con- 

 ductor has gone to pieces, and where the ship has not been 

 saved. I have not found such a case. Suppose the conduc- 

 tor is dissipated between two points [illustrating]. I found 

 this to be true in every single case of a church-tower being 

 struck where the wire runs from the bells to the clock. The 

 wire goes, and the church-tower is saved between those two 

 planes. Now, that is a matter of record. The ship "Jupi- 

 ter" had a chain conductor, and it was dissipated; and the 



