TRANSACTIONS OF SECTION A. 



601 



whether the buildings were struck during rain .or when it was not raimng. He 

 was not quite sure but that thev might learn something in that w'ay. 



There was another point which had been alluded to upon which photography 

 he thought gave very conclusive evidence ; that is, that lightning flashes are by no 

 means as instantaneous as they are usually supposed to be. First of all, most 

 people had seen lightning flashes which to their eyes appeared to last some time ; 

 but the evidence of the eyes in bright light is a little doubtful, as there are always 

 subjective ettects on the retina. Thev had a large number of photographs bearing 

 upon this pomt, and he had brought with him a very good specimen. Lightning 

 does not jump from the cloud to the air, but it goes meandering about in the air. 

 It meanders about in the air without very much rhyme or reason, and flies about 

 in a very eccentric manner. He thought it was perfectly certain that lightning, 

 when it 'was tying knots like that, could not be going with anything which in 

 orduiary parlance might be called an instantaneous speed. Of course there is no 

 such thing reaUy as instantaneity. Besides the ordinary flashes of lightning, some 

 people had seen and everybody had read about what has been called a globular 

 discharge of lightning, in which a ball of light, about the size of a cricket ball, goes 

 dancing slowly down the street and eventually discharges. It is perfectly certain 

 that between 'that very slow discharge and the quicker discharges which were 

 ordinarily spoken of as flashes of lightning there must be intermediate rates of 

 discharge. There was one point bearing upon this question of the non-mstantaneity 

 of a flash which had been adduced as evidence, but which the photographs in the 

 possession of the Committee did not contirm. In fully half of the photographs the 

 lio-htnino- does not cover the plate as a streak, but it is more or less of a banded 

 nature, something like a ribbon. It had been suggested that this apparent motiou 

 that way might have been due to a shaking of the camera. There was evidence, 

 —although he could not describe it verbally, it was easy to see it— to show that, 

 and he could not think that that evidence of the slowness of flashes was not correct. 

 Only yesterday their distinguished visitor. Dr. Janssen, made a .suggestion to him 

 which he thought furnished additional evidence of the fact. One of their most 

 remarkable photographs, besides showing three white flashes on the picture, has a 

 black flash ; that was a very curious thing. They very early got the idea that 

 that must be due to the inversion of the photograph, which sometimes took place 

 from over-exposure. Photographers knew very well that, instead of white coming 

 out as white, it came out black. It was a well-known pecuUarity of plates and 

 developers, and so on, but they were brought to a stand by the idea that this pho- 

 tograph was the only one instance that they had got, and if it should be over- 

 exposure they would have a great many over-exposed. Dr. Janssen made to him 

 the very valuable suggestion that that might be the evidence, not of a peculiarly 

 bright flash which over-exposed the plate, but of a slow moving flash which moved 

 so long that the plate was over-exposed. Of course it was impossible to say much 

 from one case. He thought it was a remarkably brilliant idea, and he only brought 

 it before them as a possible confirmation of what they were certain of from other 



Then the only other point upon which he would like to speak was not connected 

 with the photographs, but was a point upon which he would speak as a meteoro- 

 logist, that was with reference to some remarks of Mr. Preece about the height 

 of lightning clouds. He had no doubt that Mr. Preece might have seen it over a 

 sufficient amount of country. The flashes might come from a cloud only 500 feet 

 high, but that was a very low cloud, and in the majority of cases they certainly 

 came from very much greater heights. In that one particularly that he had 

 already alluded to, from the scale of the picture he was perfectly certain that the 

 lieight of that cloud was considerably over 500 feet. At the same time he miglit 

 mention that there was hardly a case of lightning much over 7,000 feet. \\ hen 

 they got on the side of mountains much over that he would not like to say too 

 precisely, but certainly a very moderate height, they always saw lightning oelow 

 it. Electrical disturbance of this kind was confined certainly to the lower 10,000 

 feet of the atmosphere. In connection with the pracrical bearing of that he might 

 mention that in Norway they had two kinds of thunderstorms. One occurred m 



