SCIENCE 



NEW YORK, APRIL 29, 1893. 



THE NEW METHOD OF PROTECTING BUILDINGS 

 FROM LIGHTNING. 



In this week's number we publish a letter on a case of 

 lightning stroke, and would take occasion to suggest that it 

 may help to clear up our ideas on these apparently erratic 

 phenomena if we constantly bear in mind that the energy, 

 just before a lightning flash, according to our present con- 

 ceptions of electricity, exists in a more or less considerable 

 mass of dielectric (the atmosphere and a portion of the 

 earth), which includes the two points between which there 

 is a difference of potential. In other words, if there is a 

 difference of potential between a cloud and the earth the 

 electrical energy exists difi'used for the most part thorough- . 

 out a mass of air extending from the cloud to the earth, 

 some, of course, existing in the surface layers of the earth. 

 Now, when the flash takes place, all will agree that this 

 energy manifests itself as light and heat, and in the knock- 

 ing- of things to pieces, perhaps. 



We can but confuse our minds if we continue to think 

 of the energy which causes the damage, or heat, or light, as 

 coming from above or below, but should rather consider it 

 as shrinking in, as it were, from all the circumambient 

 dielectric to the places where it manifests itself as a heated 

 line of air (the flash), or in the broken house-wall. The 

 energy, which is what does the harm, comes, in the case of 

 a vertical discharge not from above or below, but in the 

 main horizontally. Do not let any one misunderstand me 

 as saying that the electricity in such a case moves horizon- 

 tally, for I do not. As I pointed out in my article in Science 

 of April 8, I do not yet know of a case where the destruction, 

 by the discharge, of a small conductor has failed to protect 

 all else between two horizontal planes passing through the 

 upper and lower ends of the dissipated conductor. It may 

 be well to cite a few more cases of such protection resulting 

 from the expenditure of the energy upon a small metallic 

 conductor. 



In the Philosophical Transactions, xlix., p. 298, is a paper 

 read Dec. 18, 1755, by G. Brandir, Esq., descriptive of 

 the striking of the Danish church in Wellclose Square, in 

 which it is related that "on Monday, the 17th past, between 

 six and seven o'clock, there was, among many others, one 

 most amazing flash, accompanied with a clap of thunder, 

 that equalled in report the largest cannon ! That the next 

 morning, observing the church clock to be silent, they went 

 to the belfry, and found the wire and chain, that communi- 

 cated from the clock in the belfry to the clapper in the turret, 

 where the bells hang, to he melted ; and that the small bar 

 of iron from the clock, that gives motion to the chain and 

 wire, just where the chain was fastened, was melted half 

 through, the bar being about three-fourths of an inch broad, 

 and half an inch thick. Several links of the chain, and of 

 the wire, I have now the honor to shew you, where it will 

 be observed, that the lightning took effect only in the joints. 

 But whether it entered by communication from the wire ex- 

 posed to the air in the small turret, through the roof of the 

 belfry, or at the windows, there being several panes broke in 

 the south and west corners, I cannot say; although I pre- 



sume rather the first way, as it is very possible, that the bare 

 report of the thunder might have occasioned the latter. 



"The pieces of the wire and chain were scattered over the 

 whole belfry, nor could it be discerned, that the wood-work, 

 or aught else, had suffered." 



There is a case cited in all the books on lightning, which 

 is also interesting in this connection. The packet ship "New 

 York " was struck by lightning April 19, 1827, while in the 

 Gulf Stream. She was provided with a lightning rod, if it 

 may be so called, consisting of a pointed iron rod one-half 

 an inch in diameter and four feet long, at her mast-head, 

 from which extended an iron chain, 130 feet long, to the sea. 

 The links are described as one-quarter of an inch in diameter, 

 whatever this may mean. It is evident, however, that the 

 chain was not a heavy one and that, being a chain, it was a 

 conductor of variable resistance, a condition well known to 

 be conducive to destruction in case of the passage of a high- 

 potential current. The rod was struck. A few inches of the 

 terminal were melted, and of the chain all except three feet 

 was dispersed. The important fact here as always, so far as 

 yet known, is that no damage was done to the ship by the 

 lightning. 



My method of protecting buildings from lightning con- 

 sists simply in placing on the building, from its highest to 

 its lowest part, a small conductor of variable resistance, so 

 as to make sure of its destruction in case the house is struck. 

 And I base my confidence in its success on the fact that, 

 exercising all possible diligence in the search through the 

 records of actual cases of lightning stroke, I have not met 

 with a case of failure of such a conductor to protect, when by 

 accident it has been employed ; and, further, I have failed 

 to elicit any exceptions by the numerous methods of publi 

 cation I have employed. 



I employ one or two pounds of copper on a house of the 

 ordinary size, and if anyone will take the trouble to calcu- 

 late, according to the best data at our disposal, the energy 

 dissipated in the evaporation of a pound of copper, he will 

 understand how it is that there is none left to do further 



Another point which the records bring out, and which has 

 been noted by others, is that damage occurs near large masses 

 of metal. The small masses of metal, if not in confined 

 spaces, burn as harmlessly as gunpowder on a sheeet of 

 paper. N. D. C. Hodges. 



674 Broadway, New York. 



Spaniards are making a good many preparations for the cele- 

 bration of the four-hundredth anniversary of the discovery of the 

 the New World. In the autumn of the present year, says Nature, 

 there will be several exhibitions, in one of which will be shown 

 objects relating to the continent of America before the advent of 

 Europeans, while another will illustrate the state of civilization 

 in the colonizing countries of the Old World at the time when 

 the new continent was discovered. In October the Congress of 

 Americanists will meet at Huelva, and will discuss a variety of 

 subjects relating to the continent of America and its inhabitants 

 400 years ago. In the same month, at Madrid, a Spanish Portu- 

 guese-American Geographical Congress will meet for the discus- 

 sion of such questions as relate more particularly to the " Iberian - 

 American " races, their aptitude for colonization, and the future 

 of the Spanish language. 



