TRANSACTIONS OF SECTION A. 611 



■wire was gone. If the old-fasbioned conductors as thick as his fingers were to be 

 replaced by something analogous to bell wires he wondered what was to happen 

 after the first flash. 



Mr. Truejian Wood wanted to say one word about two of the photographs. 

 The so-called black flash, the dark flash, whatever that was, it certainly was not 

 the result of over-exposure, as had been suggested, because the white flash, which 

 was presumably on that theory less exposed, overrode the black one. Whereas, 

 of course, if the black part was a part of the plate which had received most exposure, 

 the black one would show over the white one. In that other photograph there was 

 an exactly similar dark line which was evidently the result of reflection from the 

 back of the lens, and therefore he thought there could not be the least doubt that 

 this so-called dark flash was really the result of reflection from the other flashes. 



The President : I think, gentlemen, we have now had a great deal of informa- 

 tion brought before us, and in order to finish up I will ask in the first place Lord 

 Eayleigh to make a short statement about the black flash, and then I will ask 

 Mr. Lodge to give a reply, and then Mr. Preece will have the opportunity of 

 finishing up with his remarks. 



Lord Eayleigh said he would repeat the suggestion that Professor Stokes once 

 made. He did not think it had ever appeared in print, and he was not quite sure 

 whether he ought now to mention it, but he was encouraged by Sir William 

 Thomson to do so. He thought there was no doubt, as Mr. Wood "had said, that 

 the appearance of the black flash did not suggest that over-exposure was the ex- 

 planation. Professor Stokes' view was this, he thought that under the influence 

 of a flash the atmospheric gases of oxygen and nitrogen were combined so as to 

 produce considerable quantities of the oxides of nitrogen ; that those oxides of 

 nitrogen formed therefore along the line of the flash were highly opaque to the 

 invisible rays at the upper limit of the spectrum to which most of the photographic 

 action was due, and that then when another flash occurred, illuminating the back- 

 ground of the cloud to hide the place where the first flash had been, the mark of 

 the first flash was depicted as a black line on account of its opacity to the general 

 light of the background. 



Professor Oliver Lodge said so many things had been remarked and so much 

 might be said even that had not been commented upon that one must exercise 

 caution in what one mentions. He must, however, say a few words that had 

 been suggested by the remarks of the various speakers. JMr. Walker and Mr. 

 Symons and also Mr. Preece originally had spoken as if he (Professor Lodge) had 

 e.specially attacked the report of the Lightning-rod Conference. That he had not 

 done. He had made great use of the report of the Lightning-rod Conference ; he 

 thought that they had done a very valuable piece of work. They had collected 

 together all manner of details of destructions and of failures of lightning-rods. 

 The whole of the report was bristling with failures of lightning-rods, so that he 

 was at a loss to understand — no, he did understand how it is. They said that a 

 * properly constructed ' lightning-rod never fails, because whenever a thing fails 

 they always say there is something the matter with it. They generallj- say bad 

 earth ; but why a thing ought to have such an extraordinarily good earth he never 

 could tell. What is the diflerence between one end of the conductor and the 

 other ? They stuck three points at this end and they wanted a lot of rods at that 

 end. Suppose it was reversed ; why they would have the rods in the sky and the 

 points down below. Why should one end have to be treated so very carefully 

 and the other end be left to itself? As far as protection is concerned three points 

 at the top and the three points at the bottom ought to do equally well. Of course 

 it might be inconvenient to have the ground ploughed up, and you might have 

 the ground and water-pipes broken if you have not good earth. He said they 

 ought to have a good deep earth. Flashes ought not to spit ofi' from the conductor 

 to the gas apparatus, nor to explode gunpowder, nor run along gas-pipes and play 

 the fool dancing along any part above the earth. It did not do that because it 

 met with obstruction and impedance — he did not care what they call it, a spurious 

 resistance — they might use the word resistance if they liked, but it was not what 

 they ordinarily called resistance, it was like inertia. It was like having to move 



E B 2 



