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NATURE 



[Oct. 4} 1888 



and darker than those to the eastward, and my own observations 

 upon the people of this particular district will, when they are 

 systematized, tend to define the area of this ethnical frontier 

 more precisely. It would be a remarkable result if it should 

 hereafter be shown that the physical changes observable in the 

 distribution of the existing population are in any way coincident 

 with these lines of defensive earthworks of the Roman or post- 

 Roman age : and if it should be further shown that the same 

 physical characteristics have persistently belonged to the people 

 of this region ever since the time of the Neolithic folk of the long 

 barrows, we shall find ourselves in the presence of anthropological 

 deductions of some value in their bearing on the history of 

 England. 1 purposely avoid speaking with confidence upon this 

 point, feeling certain that the necessary evidence for deciding the 

 question lies buried in the soil of the district, and will hereafter 

 be unearthed. I shall resume the inquiry as soon as the harvest, 

 if such it can be called this year, is over ; but without bias, and 

 with a mind prepared to throw over any preconceived hypothesis 

 the moment it shows itself to be untenable. 



Section A — Mathematical and Physical Science. 



Members of the Mathematical and the Mechanical Section 

 had a meeting in the rooms of Section A for the special 

 purpose of discussing the question of lightning-conductors. The 

 chair was occupied by Prof. G. F. Fitzgerald, President of the 

 Mathematical and Physical Science Section. 



Mr. W. H. Preece, President of the Mechanical Section, 

 opened the discussion, and said that if we wanted to know any- 

 thing about atmospherical electricity, we had to go back to the 

 works of Benjamin Franklin, ico years ago. Up to 1870 there 

 were absolutely no rules for the guidance of those who desired 

 to erect lightning-conductors for the protection of buildings. In 

 that year a great Conference was held on the subject, and the 

 result of its deliberations was published in a book, and included 

 a set of rules for the construction of conductors.* We had since 

 had great experience of them. He had under his supervision 

 no fewer than 500,000 lightning-conductors. Some time ago a 

 lectureship on atmospheric electricity was founded in memory 

 of Dr. Mann, who experimented on the protection of buildings 

 in South Africa. Prof. Oliver J. Lodge was selec.ed as the 

 lecturer, but, instead of cracking up the work of the Conference, 

 he took the other line, and, if his statements were true, lightning- 

 conductors would be of no use, and no buildings would be safe 

 in a thunderstorm. Prof. Lodge had committed himself to 

 fallacies which it was now his duty to bring before the meeting. 

 The Professor assumed that a lightning-rod formed part of the 

 flash. Well, it did not. Nobody had ever seen a flash of 

 lightning strike a conductor. The function of a conductor was 

 to prevent the possibility of the building being struck by the 

 flash. If it should be struck, there was some defect in the 

 construction of the conductor. Lightning did not go careering 

 wildly about, but passed along a path prepared for it. There 

 was another fallacy, viz. that a flash of lightning was instanta- 

 neous. There was no proof of that. We saw a flash of light, 

 which indicated the path of the discharge, but how long the dis- 

 charge lasted we did not know. There were invisible flashes of 

 lightning, which was proved by the fact that persons had been 

 killed under trees when there was no visible flash. He, however, 

 came to that conclusion from the effect on telegraph-wires, where 

 there were currents of sensible duration, showing that the flash 

 was not instantaneous. The next part was the hardest to discuss. 

 It was the assertion that lightning was oscillatory in its charac- 

 ter ; that it did not go direct from the cloud to the earth, but 

 went flashing backwards and forwards with considerable fre- 

 quency. This assertion was based more on mathematical reason 

 than on absolute observation, and engineers had no great respect 

 for mathematical development unless it were confirmed by abso- 

 lute experiment. The facts against the theory were that electro- 

 magnets were affected for a considerable duration of time by 

 lightning-flashes. Iron and steel were affected, and he had 

 heard letters of the alphabet signalled along the telegraph-wires 

 by a flash — the letter R which needed three signs, C which 

 needed four, and there was a case on record of G, which needed 

 eight signs. Under those circumstances the flash could not be 

 oscillatory unless the oscillations were very infrequent. A dis- 

 charge from condensers or Leyden jars might be oscillatory, but 

 they were dealing with flashes of lightning. While he was 

 attacking Prof. Lodge in that way, he must say that no one had 

 worked harder or more honestly in the matter. Prof. Lodge 



had made experiments, and they were correct, from which he 

 deduced that the self-induction of copper was greater than that 

 of iron. He also had repeated these experiments, but his deductions 

 were just the opposite. There was no doubt the Professor was on 

 the brink of a discovery. He had started a fresh hare, which 

 electricians must follow up and kill. Self-induction was called 

 up to explain all the phenomena which they did not understand, 

 and he inclined to think it was very much what the Americans 

 called a bug. In the telegraph science they had known it for 

 many years, and called it electro-magnetic inertia. The next 

 fallacy was that most conductors did not protect any area, but it 

 was known from evidence that they did. He preferred to stand 

 upon the experience of the past rather than upon Prof. Lodge's- 

 mathematical assumptions. There was a tendency to hasty 

 generalization among mathematicians, but there could be no 

 doubt that the experiments of Prof. Lodge and others were 

 opening their minds to the true nature of electricity, and that 

 they would in time be able to speak of the mechanical character 

 of electricity. They wanted to know where the energy came 

 from which was so destructive in a flash of lightning. Aqueous 

 vapour condensed and falling as rain at the rate of 1 millimetre 

 per acre per hour developed an energy of 600 horse-power per 

 acre. There was the creation of the energy which only wanted 

 further development to turn into a source of electrical energy. 

 He felt convinced that the result of that discussion would be to 

 establish the truth of the position taken up by the Lightning- 

 Rod Conference, and would bring to the front what they were 

 all anxious to see, the true theory of electricity shadowed forth 

 by Prof. Fitzgerald in his opening a 1 dress, and that would make 

 this meeting an epoch in the history of electricity. 



Prof. Oliver J. Lodge said he had no lightning-conductors 

 under his supervision, and all his conclusions were formed from 

 experiments, and if they were correct very few buildings were 

 effectively and thoroughly protected at the present time ; and, 

 further, if his views were correct, lightning-rods would in the 

 future cost very much less than now. The term electro- magnetic 

 inertia seemed to imply that they knew more than they did, s-> 

 he preferred self-induction until they attained to knowledge. 

 Mr. Preece said that no properly-constructed rod ever failed, 

 but in the report to the Conference there were a number 

 of entire failures named. He had made s >me very careful 

 experiments in which he provided alternative courses for an 

 electric current, and he found that it required less electromotive 

 force to send the current along a thin iron wire than along a 

 thick copper one. According to Mr. Preece, the object of the 

 conductor was to prevent a flash of lightning, but rods were 

 struck and melted. The conductor had two functions to perform 

 — to act as a point and prevent a flash if it could, and to carry off 

 a flash when it could not help receiving one. The electric charge 

 had some energy, and they could not hocus-pocus it out of 

 existence. It might be better to let it dribble away slowly down 

 a bad conductor than to let it rush headlong down a good one. 

 The length of flash was a question for the consideration of 

 meteorologists, and the duration of flashes was a point on which 

 the same gentlemen might do good work. He had seen flashes 

 which appeared to last two or three seconds, but he thought 

 they must have been a succession of flashes. The fact that 

 flashes deflected the compass-needle did not prove that they 

 were not oscillatory, nor did it prove anything as to their 

 duration. A momentary flash might produce the same effects. 

 There was the question of a flash magnetizing a bar of steel. 

 An oscillating current was able to do that ; although Prof. Ewing 

 used an oscillating current to demagnetize steel. The discharge 

 of a Leyden jar caused an oscillating current. The charging 

 was like lifting a pendulum rod suspended freely at one 

 end. When the jar was discharged it was like releasing 

 the pendulum ; it must oscillate, and so must the electricity, 

 and its oscillation would vary in accordance with the friction 

 and other modifying causes. The greater the electro-magnetic 

 inertia, the more certainly would there be oscillation. With 

 regard to the protection of areas, the area which Mr. Preece 

 imagined as protected was so small that they might give it 

 him without discussion. There was, however, in his opinion 

 no sure area of protection. Mr. Preece might have pressed 

 him hard on the question of the conditions of a flash. He 

 (the speaker) had assumed that the flash behaved as electricity 

 did in an experiment. The cloud, however, was not like the 

 tinfoil of a Leyden jar ; it was made up of globules with 

 spaces between them, and a discharge might be more like that 

 of a spangled jar, or might be dribbled away a bit at a time, and 



