Oct. ;, ij 



SCIENTIFIC NEWS. 



369 



into the rotating armature, as it is called, and less wire 

 on it, by shortening the stationary magnet, and generally 

 by concentrating the magnetic action, these constructors 

 have raised the commercial efficiency of these machines to 

 actually as high as between 93 and 94 per cent. ; further, 

 how by recognising the force of the general principles laid 

 down by Professor Perry and myself as to the difference 

 that should exist in the contruction of a motor and a 

 dynamo Messrs. Immisch have succeeded in constructing 

 strong durable electro-motors weighing not more than 

 62 lbs. per effective horse-power developed. 



The subject is so entrancing to me, the results com- 

 mercially so important, that I am strongly tempted to 

 branch off, but the inexorable clock warns me that I 

 must concentrate my remarks as they have concentrated 

 the magnetic action. 



Of the power put into an Edison Hopkinson 

 dynamo 87^ per cent, has actually been given out by the 

 motor spindle, when 50-horse power was being trans- 

 mitted. How does this compare with combined efficien- 

 cies of an air pump and an air motor, or of a water 

 pump and a water motor? I understand that in either 

 of these cases 60 per cent, is considered a very satis- 

 factory result. As far, then, as the terminal losses are 

 concerned, electric transmission of power is certainly 

 superior to air or water transmission. 



The next point to consider is the loss of power on the 

 road 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. Biggs and Brittle at the Institution of 

 Civil Engineers in 1878, and that problem was con- 

 sidered 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 electric motors 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 realisation 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 same small current 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 Down supplies the current for each 

 of the two circuits. 



The electric pressure, or potential difference, between 



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 unpleasant shocks. This 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 

 system, which cripples all attempts at mechanical street 

 locomotion, because we are Conservative 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 

 prohibit the eating of dinners because some people 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. Reckenzann tells me, possesses 300 miles of ordinary 

 tramway track, and Philadelphia city 430 miles, so that 

 there is more tramway line in these two 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 fifty miles 

 an hour round a curve, with only a bit of iron rail be- 

 tween him and eternity, would be far too risky to be 

 even contemplated. And yet we do go in express trains, 

 and even eighty miles an hour is beginning to be con- 

 sidered not to put too great a demand on the funds of 

 life insurance companies. The American plan of basing 

 a conclusion on experience rather than 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 num- 

 ber of people that have suffered in consequence — not a 

 single person, I am assured, outside the companies' staff, 

 we are compelled to conclude that high potential now is 

 what thirty miles an hour was half a century ago — un- 

 canny rather than dangerous. 



But it is possible to use a very large potential dif- 

 ference between the main wires, by means of which the 

 electric power is economically conveyed a considerable 

 distance, and transformed into a small potential difference 

 in the houses where it is utilised. An electric trans- 

 former 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 



