October 19, 1905J 



NA TURE 



615 



were arranged for at 33,000 volts — the one at Crofton, 

 California, and the other at Redlaijds, California; and 

 MO |)rfssure higher than that used on the Lauffen-Frank- 

 fort transmission seems to have preceded this 33,000 volts 

 imywhere in the world. Indeed, it would almost appear 

 as if electrical engineers were waiting to use a higher 

 pressure than 25,000 volts until the publication of the 

 census of Johannesburg. 



In 1898 the highest working pressure in the world was 

 40,000 volts for a 34-mile transmission at Provo, in Utah, 

 and the male white population in Johannesburg was also 

 about 40,000. Then came the war, and volts beat white 

 man, for, according to the census of last year, while the 

 white male population was 52,106, there were several 

 examples of transmissions at 60,000 volts, as seen from the 

 following table. 



I>ut with the influx of the white members of the British 

 .X^sociation doubtless the tide will turn, white man will 

 make a spurt and catch up electric pressure, and in this 

 respect, at any rate, the Witwatersrand will become a 

 white man's country. 



Indeed, not only have various successful 6o,ooo-volt 

 transmission schemes been carried out, but the Kern River 

 Power Company in California is constructing one for 

 transmitting 4020 horse-power over no miles at 67,500 

 volts. 



Transmission at 67,500 volts over no miles. Why, when 

 the new railway — Brakpan to Witbank — is completed, no 

 miles will be 20 more than will separate the Rand from 

 the coalfields at Witbank — fields that produce such good 

 coal that the Central South African Railways have con- 

 tracted to purchase 84,000 tons during this year, at six 

 shillings per ton at the pit's mouth. Now, at a pressure 

 of 67,500 volts, these two small wires could, without 

 becoming too warm, bring about 9000 horse-power from 

 Witbank and deliver 7600 of it to the Rand. 



Or if six wires were used like those now employed by 

 the Rand Central Electric Works, then, at 67,500 volts, 

 9000 horse-power might be put in at Witbank and only 

 5 per cent, lost on the road, that is, about 8550 horse- 

 power delivered on the Rand. 



But the insulators would have to be placed much farther 

 apart than on the existing Rand posts to prevent the start- 

 ing of a brush discharge between the wires — a subject to 

 which I will return. 



You will now grasp why in 1895, ten years ago, it was 

 a bold and pioneering policy to equip the Rand Central 

 Works for 10,000 volts, and to use 13,000 volts during 

 times of full load, and why in 1905 the recommendation 

 of some advisers to distribute power at only 10,000 volts 

 to the proposed substations of the contemplated 57 miles 

 of electrified railways — Springs to Randfontein — is most 

 retrograde of those advisers to the railway. 



In 1879, a firm of electrical contractors, well known 

 then, and equally well known now, told me that they had 

 been asked to tender for the construction of an electric 

 transmission system to convey a comparatively small 

 amount of power 10 miles. But since they considered that 

 they could not possibly hope to deliver more than half, 



NO. 1877, VOL 72] 



while, in practice, they feared that they would only succeed 

 in delivering much less, the proposal had to be ranked 

 with the exploits of Gulliver and Baron Munchausen, and 

 so even that firin declined to tender. To-day, twenty-six 

 years later, electric power is, from an engineering and 

 from a business point of view, being successfully trans- 

 mitted 232 miles — nearly as far as some of you took 

 fifteen hours the night before last in being transmitted 

 from Ladysmith. 



Now, how are these electric pressures of 10, 20, 30, 40, 

 50, 60,000 volts produced? Why, by means of the alternate 

 current transformer, which does for electric power exactly 

 what the lever does for mechanical power. Exert a small 

 force through a long distance at the long end of this lever, 

 and you have a large force e.xcrted through a short 

 distance at the short end. Apply a small electric pressure 

 with a large current at one side of this transformer, and 

 you have a large pressure with a small current at the 

 other. But there are no moving parts, therefore the 

 arrangement is called a " static transformer." It requires 

 no adjustment from day to day, therefore it may be kept 

 entirely immersed in oil to improve its insulation. 



Such statical transformers I used to step up the pressure 

 from 100 to 20,000 volts at the transmitting end, and to 

 step down the pressure from 20,000 to 100 volts at the 

 lamp end in the last experiment. Everything looked quite 

 harmless until I intentionally brought the transmission 

 wires into contact. So does the transformer, immersed in 

 a huge cylinder of oil, now projected on the screen, 

 although it regularly produces 60,000 volts, and can supply 

 1 100 horse-power at that pressure. So does this water- 

 cooled transformer (the interior of which is seen in an 

 X-ray picture to the right, and the exterior to the left), 

 although it can supply 2000 kilowatts, that is, 2700 horse- 

 power. Its size can be realised by comparing it with the 

 tiny transformer by its side — the size of the one which I 

 have on this table. 



60,000 volts, well, what of it? some of you may say. 

 It cannot start a discharge betw-een even sharp needle 

 points separated by a greater distance than about si.x 

 inches, and some of vou have produced such a spark with 

 an electrical machine — I am producing such a one now. 



But each time that a spark passes between the terminals 

 of the electrical machine the pressure is relieved, so no 

 arc is maintained. Bring the terminals of that transformer 

 within si.x inches of one another, however, and a roar- 

 ing arc of 2700 horse-power will be kept up, dealing de- 

 struction around. 



Let me show you a spark started with a 70,000-volt 

 transformer when supplied with only one horse-power. 

 What a banging is produced. Now picture to yourselves 

 what would be the result if the power were not of one, 

 but of 2700 horses, such as that transformer can furnish. 



The photographs show the sort of discharge that may 

 occur over the surface of an insulator i foot high — such 

 as is used on a high voltage transmission line — when the 

 testing voltage is 80,000 in this case and 105,000 in that, 

 and when there is plenty of power to maintain the arc. 

 It is veritable lightning, not a mere flash, but a continued 

 flame ; and the sort of insulator that is used in practice 

 for a 70,000-volt transmission is realised by looking at the 

 specimens, w'hich are only intended for 10,000 volts. 



There is nothing new in high voltage by itself — it existed 

 in the period of the frictional electrical machine more than 

 100 years ago, but it was associated with only a very small 

 current ; next, dating from the development of the dynamo, 

 came the low voltage large current period ; and now we 

 have entered on a third era, the high pressure moderate 

 current period, that is, the period of high pressure com- 

 bined with horse-power. 



Next I come to a very important question, and one that 

 merits far more consideration than it has yet received. 

 There are two kinds of electric current — direct current 

 and alternating current. Direct current is like a con- 

 tinuously flowing stream of water, such as, for example, 

 the one that flowed through this pipe and drove this 

 turbine. Alternating current, on the contrary, is like this 

 band, which, although swinging backwards and forwards, 

 also turns a wheel in one direction at the other end. Now, 

 which kind of electric current should be used for the dis- 



