Sept. 27, 1888] 



NA TURE 



533 



By taking such observations as these in different places it is 

 possible not only to determine the height at which they enter but 

 the velocity with which they pass through the upper regions of 

 the air, even supposing they do not eventually get to the bottom. 

 The lowest velocity determined up to the present time is some- 

 thing like 2 miles per second ; the maximum is something like 

 50 miles a second ; but we may say that the average rate of 

 movement is 30 miles a second, which is about 150 times faster 

 than a shell leaving one of our most powerful guns. 



J. Norman Lockyer. 

 ( To be contimied.) 



THE ELECTRIC TRANSMISSION OF PO \VER> 

 II. 



"PHE next point to consider is the loss of pov\er on the road 

 A between the dynamo at the one end and the motor at the other. 

 This problem was perhaps seriously attacked for the first time in 

 the discussion of a paper read by Messrs. Higgs and Brittle at 

 the Institution of Civil Engineers in 1878, and that problem was 

 considered in some detail theoretically and experimentally at the 

 lecture I gave during the meeting of the British Association in 

 Sheffield in the following year. It was then shown that, since 

 the power developed by the generator and motor depended on 

 the product of the current into the electric pressure, while the 

 loss when power was transmitted through a given wire depended 

 on the square of the current and was independent of the electric 

 pressure, the economical transmission of power by electricity on a 

 large scale depended on the use of a very large electric pressure and 

 a small current, just as the economic transmission of much power 

 by water depended on the use of a very large water pressure and a 

 small flow of water. At that time it was not thought possible 

 to construct a small dynamo to develop a very large electric 

 pressure) or potential difference as it is technically called, and 

 therefore it was proposed to join up many dynamos in series at 

 the one end and many lamps or electromotors in series at the 

 other, and to transmit the power by a very small current, which 

 passed through all the dynamos and all the lamps in succession, 

 one after the other. 



You have an example to-night of the realization of this 

 principle in the fifteen arc lamps that are all in series outside 

 this Drill Hall, and are worked with a small current of only 6 '8 

 amperes, as indicated in the wall diagram ; and a further example 

 in the thirty arc lamps at the Bath Flower Show, which are also 

 all worked in series with the small cm rent passing through 

 them ; but it is known now how to produce a large potential 

 difference with a single dynamo, so that a single Thomson- 

 Houston dynamo belonging to Messrs. Laing, Wharton, and 

 I )own supplies the current for each of the two circuits. 



The electric pressure, or potential difference, between the 

 terminals of any arc lamp is not high, but it is between the main 

 wires near the dynamo as well as between these wires and the 

 ground. How far does this lead to the risk of sparks or un- 

 pleasant shocks ? That is a point that can be looked at in a 

 variety of ways. First, there is the American view of the matter, 

 which consists in pointing out to people exactly what the danger 

 is, if there be any, and training them to look out for themselves : 

 let ordinary railway trains, say the Americans, run through the 

 streets, and let horses learn to respect the warning bell. Next, 

 there is the semi-paternal English sy.-tem, which cripples all 

 attempts at street mechanical locomotion, because we are con- 

 servative in our use of horses, and horses are conservative in 

 their way of looking at horseless tramcars. Lastly, there is the 

 foreign paternal system, which, carried to its limit, would pro- 

 hibit the eating of dinners because so ne people have at some 

 time choked themselves, and would render going to bed a penal 

 offence because it is in bed that most people have died. 



We laugh a good deal at the rough-and-ready manner adopted 

 on the other side of the Atlantic. The Americans, no doubt, 

 are very ignorant of the difficulties that properly-minded people 

 would meet with, but it is a blissful ignorance where it is folly 

 to be wise. Every English electrician who has travelled in 

 America comes back fully impressed with their enterprise and 

 their happy-go-lucky success. They have twenty-two electric 

 tramways, carrying some 4,000,000 passengers annually, to our 

 four electric tramways at Portrush, Blackpool, Brighton, and 

 Bessbrook. Why, New York city alone, Mr. Rechenzaun tells 

 me, possesses 300 miles of ordinary tramway track, and Phila- 

 delphia 430 miles, so there is more tramway line in these two 



1 Lecture delivered by Prof. Ayrton, F.R.S., at the Di ill Hall, Bath, on 

 Friday, September 7, :888. Cont.nued from p. 511. 



cities than in the whole of the United Kingdom put together. 

 Now there would be no difficulty in proving, to anyone un- 

 familiar with railway travelling, that to go at 50 miles an hour 

 round a curve with only a bit of iron between him and eternity 

 would be far too risky to be even contemplated. And yet we 

 do go in express trains, and even 80 miles an hour is beginning 

 to be considered not to put too great a demand on the funds of 

 life insurance companies. The American plan of basing a con- 

 clusion on experience rather than on anticipations is not a bad 

 one ; and if we follow that plan, then, taking into account that 

 there are 75,000 arc lights alight every night on the Thomson- 

 Houston high-potential circuits throughout the world, and the 

 comparatively small number of people that have suffered in con- 

 sequence (not a single person, I am assured, outside the com- 

 panies' staffs) we are compelled to conclude that high potential 

 now is what 30 miles an hour was half a century ago — uncanny 

 rather than dangerous. 



But it is possible to use a very large potential difference 

 between the main wires by means of which the electric power is 

 economically conveyed a considerable distance, and transformed 

 into a very small potential difference in the houses where it is 

 utilized. An electric transformer is equivalent to a lever, or 

 wheel and axle, or any other of the so-called mechanical powers. 

 You know that a large weight moving through a small distance 

 can raise a small weight through a large distance ; there is no 

 gain in the amount of work, but only a transformation of the 

 way in which the work is done. A large weight moving through 

 a small distance is analogous with a high potential difference and 

 a small current, while a small weight moving through a large 

 distance is analogous with a small potential difference, and a 

 large current, and an electric transformer is for the purpose of 

 effecting the transformation with as little loss as possible, so that 

 what is lost in potential difference may, as far as possible, be all 

 gained in current. 



Electrical transformation may be effected by (1) alternate 

 current transformers, (2) motor-dynamos, (3) accumulators, or 

 secondary batteries, (4) direct-current transformers. Of these 

 apparatus, the eldest by far is the alternate-current transformer, 

 as it is merely the development of the classical apparatus in- 

 vented by Faraday in 1831, and familiar to many of you as the 

 Ruhmkorff, or induction-coil. A combination of a motor and 

 dynamo was suggested by Gramme in 1874. Accumulators are 

 the outcome of Plante's work, while direct-current transformers 

 are quite modern, and not yet out of the experimental stage. 



After studying the literature on this subject, it appears, as far 

 as I have been able to judge, that the first definite proposal to 

 use a high potential difference in the street mains, and transform 

 down to a low potential difference in the houses, was made in 

 the lecture given by me at the meeting of the British Associa- 

 tion in Sheffield in 1879, on which occasion I explained and 

 showed in action the motor-dynamo principle suggested by Prof. 

 Perry and myself. The apparatus on the platform is not unlike 

 that shown on the former occasion : an Immisch motor working at 

 500 volts, and with a current of 6'8 amperes, is geared direct to a 

 Victoria Brush dynamo giving five times that current, and we 

 will now use this larger current to produce an electric fire. 

 [Experiment shown.] Messrs. Paris and Scott have combined 

 the motor and dynamo into one machine, which they have 

 kindly lent me, and by means of which we are now transforming 

 about 700 volts and 6 '8 amperes into 100 volts and about 40 

 amperes used to light that group of sunbeam incandescent lamps 

 or work these motors. [Experiment shown.] 



Lastly, here is a working illustration of the double transform- 

 ation proposed by MM. Deprez and Carpentier in 1881, by 

 means of which — while the potential difference between the 

 mains may be 2000 or 10,000 volts, if you like — not merely is 

 the potential difference in the house so low that you could hardly 

 feel anything if you touched the wires, but, in addition, there 

 is the same security against shocks in the dynamo-room. This 

 alternate-current machine is producing about 50 volts, which is 

 transformed up to 2000 volts by means of this transformer. At 

 the other end of the platform, by means of a similar transformer, 

 the 2000 volts is transformed down again to 50 volts, em- 

 ployed to light that cluster of low-voltage incandescent lamps. 

 [Experiment shown.] For the use of this apparatus I am 

 indebted to the kindness of the Anglo-American Brush Company. 



In this experiment there is, as a matter of fact, still more trans- 

 formation than that I have yet mentioned, because, whereas in 

 actual practice the alternate-current dynamo, as well as the small 

 dynamo used to produce the current for magnetizing the electro- 

 magnets in the alternate-current dynamo, would be worked by 



