TRANSACTIONS OF SECTION A. G13 



rod Conference Report, gives in Appendix K a list of conductors wliicli had been 

 melted by the flash, and he apologises for the shortness of the list. No apology- 

 was necessary, for they very seldom got melted, and if they were to analyse those 

 Mr. Symons gave they would find in every case that the upper terminals had been 

 melted (as they might have expected) and not the full length of the conductor. 

 There was only one case, and that was of a bell- wire. When bell-wires were used 

 then they were melted, but he did not want wires to be put up which were of the 

 thickness of bell-wires. 



Iron buildings, as Sir William Thomson had said, are practically safe for 

 ■powder magazines. They are the safest things that could be made, but even with 

 them some little care must be taken ; the iron must be in absolutely good connec- 

 tion all through. If there is a gap left anywhere there may be a spark at that gap. 

 'When an iron building is struck they might have the electricity surging about in 

 all directions, and they might get sparks in the most unexpected places and for the 

 most apparently ridiculous reason. The gap might be only half an inch long or a 

 quarter of an inch long, but that would be quite sufficient to hght the gas and do 

 all the damage. It was that danger in the case of gas and in powder magazines 

 of having gaps only a quarter of an inch long, and they might get them where they 

 least expected them. 



As regards the possible effect of sound waves he would just call attention to 

 one little experiment which was not his at all — it was first made by Dr. Guthrie, 

 but it had been called attention to at the Physical Society afresh and independently 

 bv Mr. Cooke, he thought. They took a discharging Leyden jar, which, as he had 

 often said, gives ether waves of a calculable length. Now this modification of the 

 ■experiment had been made by his friend Mr. Chattock. That gentleman took a 

 little tube like a resonant tube, sprinlded powder in it, and when the spark crossed 

 near the mouth of that tube it was drawn into it like the ripples in the sand, 

 indicating that a longitudinal wave had done that. These longitudinal waves were 

 extremely short, about a millimetre in length. Sound waves are practically one- 

 millionth of a light wave. That was evidence of the oscillation. The spark is 

 subject to longitudinal waves due to vibration sound waves, about a millimetre long, 

 which throw the sand into ripples. It may be those longitudinal sound waves of 

 which Sir William Thomson spoke which may from some action or other precipitate 

 a response in the neighbourhood, thougli no "doubt there are other causes too. 



Mr. Preece said he would not occupy their time much, because there would be 

 other occasions when the points at difierence between them would be argued. He 

 might say they had dwindled down to a very small thing indeed. As regarded the 

 question of iron and copper, in an.swer to Sir William Thomson, most, in fact all, 

 of those lightning-protectors of which he had actual experience were of iron, and 

 he had always been, as most of them knew who had read the reports he had 

 written, a great advocate of iron. He thought the use of copper to the extent to 

 which it was used introduced a needless expense into the erection of lightning- 

 protectors. His own impression was that every private house could be thoroughly 

 protected, according to the recommendations of this Lightning-rod Conference, 

 for at most a pound. Anybody could buy a coil of stranded iron rope, and it' they 

 took an iron rope about a quarter of an inch in diameter, with the finial Mr. Synions 

 had referred to, he believed that they could safely protect their houses with lightning- 

 protectors for a few .shillings, instead of now, where copper was employed, 

 indulging in the expenditure of a few pounds. 



The President said he was sure they had all heard with very great pleasure 

 this discussion that had taken place, and it was with very great diffidence indeed 

 that he felt called upon by his position as President rather than by any desire to 

 do so to say a few words in summing up what seemed to him the result of the 

 discussion. " He was glad to say that he had had no experience of lightning. It 

 was not an agreeable thing to have anything to do with. However it was most 

 closely allied — there was no doubt about it — to static electricity, which he had 

 heretofore looked upon as one of the most beautiful but useless adaptations of 

 nature, and he hoped now that these experiments with what had been called 

 static electricity would gain fresh interest from the practical applications that 



