October 19, 1905] 



NA TURK 



617 



ing. Again, in the case of the 150 miles transmission, at 

 50,000 volts, by the Bay Counties Power Company, in 

 California, it was found that lb charge even the aerial 

 lines as a condenser required 40 amperes, so that the 

 current flowing into the system remained practically un- 

 changed when the useful load was decreased from several 

 thousand horse-power down to nought. 



Now this is the very opposite of the effect we previously 

 noticed, for in that case it was the alternating pressure 

 that left the lumps dull by failing to send enough current 

 into the transmission system. .Surely, then, the one effect 

 i- a correction of the other. That is so, and I will give 

 you a practical illustration. 



1 have here two transmission lines, the one with its 

 going and return conductors placed far apart so as to 

 exaggerate the first effect, the other with its going and 

 return conductors near together to exaggerate the second 

 effect ; indeed, as I am employing for this experiment 

 only a pressure of 100 volts, there is no risk of brush dis- 

 charge, and so I have put the wires extremely near together 

 on the second transmission line. The alternating current 

 produced by the dynamo divides itself between the two 

 transmission lines, and the two branch currents are about 

 equal. 



But, as you may see by means of the oscillograph — an 

 instrument developed in my laboratories by Mr. Duddell, 

 one of my students, for giving ug a picture of the current 

 and pressure waves in each of the two circuits — there is a 

 great difference between the waves in the two circuits. In 

 the transmission line with the wires far apart, the reversals 

 of the alternating current occur after the reversals of 

 applied pressure, the crests of the current wave lag behind 

 the crests of the pressure wave, whereas in the case of 

 the transmission line, with the wires very near together, 

 the e.xact opposite occurs, viz. the crests of the current 

 wave are in advance of the crests of the pressure wave. 



Now, in the circuit coming from the dynamo, both 

 current waves e.xist together, and as the crests of the one 

 wave coexist with the troughs of the other there is inter- 

 ference, and the result is practically no current at all. 

 So here we have the rather surprising result of practically 

 no current in a main circuit, and yet a considerable current 

 in each of the branch circuits into which the main circuit 

 divides. 



This may perhaps be regarded as a beneficial result, and 

 .should be added to the score of alternating current. But 

 just as a very small alternating current in the main circuit 

 can be split up into two large currents in the branch 

 circuits, a small alternating pressure can be split up into 

 two large alternating pressures, and in that case the result 

 must be scored against the use of alternating current. 



In this experiment I use also two circuits, one with 

 the conductors very far apart, and the other with them 

 very near together ; but instead of employing these circuits 

 as two branch transmission lines I put them end on, so 

 that they constitute successive portions of the same trans- 

 mission line. An alternating pressure of only 100 volts is 

 provided by the dynamo and applied to the whole arrange- 

 ment, and yet you observe that, between the going and 

 return conductors in that part of the circuit in which they 

 are far apart, as w-ell as in that part in which they are 

 rear together, a pressure exists of 2400 volts, which is 

 twenty-four times as great as the entire pressure supplied 

 by the dynamo to the mains. 



This result with alternating electric pressures is not 

 unlike that obtained with mechanical forces when a small 

 force is resolved into two very large ones, with each of 

 which it makes nearly a right angle. 



Much damage has been done to electric cables, used for 

 the distribution of power, by these unexpected high 

 pressures produced by resonance in alternate current 

 circuits. A cable may have been tested at twice or thrice 

 the working pressure and passed as satisfactory. But if 

 there is a liability of a pressure being applied, which, as 

 you see, may in somewhat extreme cases be twenty or 

 thirty times the working pressure, what avails it that 

 there is a factor of safety of 2 or 3?^disaster must follow. 



Now with direct current for long distance transmission 

 there is no question about the electric pressure at the top 

 and bottom of a wave being much greater than the mean 

 pressure,' no question about self-induction reducing the 



NO. 1877, VflL. 72] 



current — no objection, therefore, to putting the conductors* 

 as far apart as the risk of brush discharge may necessitate 

 — no question about capacity current, no resonance 

 troubles, S:c. 



I wonder whether any of you are thinking — Well, perhaps 

 there may be something in this heresy after all. No? 

 Oh ! then you are thinking, if the arguments were sound, 

 the direct current system would have been already 

 employed for long distance transmission. Well, but it has ! 

 Power up to 3000 horse has been transmitted with direct 

 current, at 14,000 volts, from Combe Garot to Le Locle and 

 La Chaud de Fonds, round a circuit 32 miles long ; 4600 

 horse-power has been transmitted w'ith direct current, at 

 23,000 volts, 35 miles from St. Maurice to Lausanne ; and 

 a transmission system for 6000 horse-power, at 60,000 volts, 

 over 114 miles from Moutiers to Lyons, is in course of 

 construction. 



Another advantage that is possessed by all these examples 

 of direct current transmission carried out by M. Thury 

 is that it is the current that is kept constant and the 

 electric pressure that is automatically raised when (he 

 demand for power is increased, whereas with the ordinary 

 alternate current system it is the pressure at the lamp end 

 that they aim at keeping constant, and the current that 

 varies automatically with the demand for power 



Now it is far more easy to maintain the constancy of 

 the current flowing round a long circuit than to prevent 

 the bobbing up and down of the electric pressure at the 

 distant end of a long transmission line, and that irritating 

 dancing of the lights, with which Johannesburg is so 

 familiar, would be particularly difficult to avoid if the trans- 

 mission line were long and the electric pressures at its 

 two ends differed by some thousands of volts. 



Constant current has also its well known disadvantages, 

 but these would not come into play if the constant current 

 were not taken into houses, mines, &c., but used to drive 

 motor generators in substations, the dynamo portion of the 

 motor generator being of any type desired. 



The pioneering development that American boldness, 

 enterprise, initiative, and originality have brought about 

 in the electric distribution of power, combined with the 

 extraordinary commercial success that it has won on both 

 sides of the Atlantic, have made people ask, " Is such an 

 industrial revolution in store for South Africa? " 



At first sight one is inclined to answer " No ! " This 

 country is dotted with coalfields — coalfields blacken the 

 map, and the produce of some of them is reported to be 

 nearly equal to the best Welsh coal in quality. A 

 humorous English paper said that I was going to give 

 this lecture standing on a coal waggon to indicate how 

 superior, as a carrier of energy, was a coal cart to a 

 current. 



When, on the one hand, one hears that good coal is 

 brought from Witbank and delivered to the mines on the 

 Rand at 13s. a ton, and that even this price will be 

 lowered on the completion of the new railway from Wit- 

 bank to Brakpan, one feels that long distance electric 

 distribution has not much chance — indeed, a proposal to 

 burn slack coal at Vereeniging, only 33 miles from 

 Johannesburg, and electrically distribute the power on the 

 Rand, fell through. . 



On the other hand, when one finds that at the \\'ankei 

 coalfields themselves large coal costs 15s. a ton rt the 

 pit's mouth, and that .Salisbury pays 365. 5<i., Umtali 

 43s. (td.. and Kimberley 6ys. per ton, one feels that electric 

 distribution in this country possesses possibilities. 



South W'ales has many coal mines — cheap slack coal lies 

 heaped at the pit's mouth. Let me put this question to 

 you : " If an electric supply distributing company were to 

 start in South Wales to obtain their electric energy, not 

 from waterfalls, mark j-ou, but from coal brought to their 

 generating stations from coal mines, would you anticipate, 

 I ask, that such a company would obtain customers for 

 their electric energy at coal mines themselves? " " No, 

 emphatically no," you would reply, for that would be 

 taking coals to Newcastle with a vengeance. Yet, 

 what does that map tell us? \\"hy that, within four years 

 since that South Wales company was merely applying to 

 Parliament for an Act to enable them to establish a dis- 

 tribution of power system, fourteen of the largest colliery 



