612 REPORT— 1888. 



a great weight ; there is no resistance to its motion, you may knock it about with 

 a hammer and expect it to fly to the other end of the room, but it does not move, 

 although you may knock the hammer to pieces and do a great deal of damage to it. 

 That was the kind of obstruction that was met witii in the lightning-conductor. 

 As regarded the failures of properly constructed lightning-conductors he wanted ta 

 know from Mr. Symons (there would be plenty of opportunities for continuing 

 this discussion in print) why had M. Melsen's Hotel de Ville at Brussels got set 

 on fire by a lightning flash ? because if anything is well protected and admirably 

 and thoroughly protected according to orthodox principles that building was safe. 

 He (Professor Lodge) thought it was protected too. When he spoke of its not 

 being completely safe he did not mean, and he never thought of meaning, that 

 lightning-conductors are of no use. They are of very much use, but they may 

 occasionally and be believed do occasionally fail. M. de Fonvielle spoke of the 

 great experience Mr. Preece had had and also of the great experience that they 

 had had in Paris with all manner of conductors ; for lightning-posts and things- 

 like that they did not fail much. But then a lightning-post and an obelisk and a 

 lighthouse even are the easiest possible things to protect ; there is just the one 

 column and if you stick one protector down there is not much chance of its splitting, 

 or of its doing much damage to anything else. In the Monument of London the 

 handrail of the staircase, he believed, is the lightning-conductor ; he did not know 

 what it would feel like when it was struck ; he dared say it had been struck, 

 probably in the night when nobody was there, but he believed it had not been 

 damaged in the least bit. It was not much use to protect powder magazines and 

 houses where there is escaping gas. If the lightning flash went down near a leaden 

 gas-pipe it would very likely fuse the pipe, and they would have the house burnt 

 down. They might not know that the house had been struck, but they would 

 wake up in the morning and find themselves burnt. 



Professor Forbes asked him to say why he did not use one pairof Imobs instead 

 of two pairs of knobs to try the experiment with. If Professor Forbes tried the 

 one pair of knobs he would find that he could not perform the experiment at all ;. 

 there must be two pairs of knobs somewhere. 



With these oscillating currents, which are of extremely great frequency (there 

 are something like a million a second), it is only the outer surface that is obstructed > 

 It is due to the space surrounding the conductor, and it is not due to the material 

 of the conductor. Itis the tube of the conductor that flies ; therefore the conductor 

 does not get magnetised at all, whether iron or copper ; the thing does not care 

 about its permeability, its magnetic properties, or its conductivity much. The- 

 current is very great even from an ordinarv Leyden jar ; the current produced 

 when discharging is about ."jjOOO amperes. The current in a lightning flash is, no- 

 doubt, enormous ; he should think a million amperes for the time it lasts. That it 

 is very great is shown by the heating powers and the destructive powers that it has,, 

 only the duration is so extremely small. Hence it is that the impedance is so very 

 great, because there was a certain amount of ohms, and then there was a tremendous 

 current, and so they got the tremendous difference of potential at the end and the 

 liability to spit oflT. Seeing that only the outer surface conducts, what is the good 

 of the inside of the rod? It may have to conduct the heat away, and so prevent 

 the heating, or it may not have time to do that; probably there is no particular 

 good in it, but if they were going to have a tube they had better have a flat tube, 

 and it was also better to have a strand of separated wires or have a series of wires 

 about the size of telegraph wires. Mr. Preece knew very well that the iron light- 

 ning-conductors on the telegraph posts protected them, and a house would be pro- 

 tected in a similar way, and chiefly by putting a great number of common galvanised 

 wires up. That was his view, but it was not authoritative. If what he said was 

 authoritative, and would be sent forth as a statement made in that room, of course 

 he would hold his tongue ; but of course one simply said that which one thinks at 

 the time. It is found that all the failures of lightning-conductors are due to the 

 spitting off^, are due to this high potential, are due to the impedance of it, the 

 obstruction of it — to the fact that it does not conduct so easily as they would 

 expect it to do, and not due to the melting of it. Mr. Symons, in his Lightning- 



