November 29, 1894] 



NATURE 



109 



Greenwich a few nights afterwards (Bode had in the 

 meantime, in company with an amateur astronomical 

 friend, detected it at Berlin on November ii, four days 

 after Miss Herschel's discovery at Slough), contested 

 this view on the ground that the nucleus might be 

 situated not in the apparent centre of the comet. And 

 this indeed would seem to be the case ; the general 

 appearance of the comet, when seen under the most 

 favourable circumstances, being that of a slightly oval 

 vaporous mass, with a small ill-defined nucleus 

 eccentrically situated within the coma. In 1848, 

 towards the end of September, a faint brush of light was 

 noticed by Prof. Bode, extending from the more con- 

 densed part of this towards the sun ; and a few weeks 

 afterwards a tail, between one and two degrees in length, 

 was seen on the other side, i.e. the normal position of a 

 comet's tail. Late in the month of November in the 

 same year, it may be remarked, the comet made one of 

 its very near approaches to Mercury, coming within the 

 distance 003S of the Earth's mean distance from the 

 sun, or about three and a half millions of miles. The 

 return of 1871 was a noteworthy one in several respects ; 

 and particularly for the remarkable fan-like appearance 

 which the coma presented in November and December. 



The apparent contraction of a comet's bulk as it ap- 

 proaches the sun, and dilatation of it again when receding 

 from him, which has been manifested in several of these 

 bodies, has been especially marked in the case of 

 Kncke's, the visible diameter at perihelion being not 

 ecjual to the twentieth part of what it is about the time 

 when the comet first comes into view. The most probable 

 cause of this would seem to be that suggested by Sir 

 John Herschel, which would make it rather apparent 

 than real, namely, that near the sun a part of the cometary 

 matter becomes invisible by evaporation, just as a cloud 

 of fog might be. 



In 1871 the spectrum of this comet was examined by 

 Prof Young, and found to consist of three bright bands, 

 of which the central one was the most prominent ; they 

 were somewhat sharply defined on the least refrangible 

 side, whilst on the other they were diffused. " Of a 

 continuous spectrum there was no trace, and the spec- 

 trum was the same from every part of the comet.' But 

 in 1S81 a faint continuous spectrum was detected by Prof 

 Tacchini, so that the result of spectrum analysis applied 

 to this comet would seem to be essentially the same as 

 that obtained from the great majority of comets of which 

 the light has been examined in this way. 



At the last appearance of Encke's comet, in 1891, it 

 was first seen by Prof. Barnard at the Lick Observatory 

 in California, at the beginning of August, and passed its 

 perihelion on October iS. At the present return it was 

 detected at the Nice Observatory on October 31, in the 

 constellation Pegasus ; and Dr. Max Wolf found it 

 registered on a photographic plate taken by him the same 

 evening at Heidelberg. As on several previous occasions, 

 its ephemeris has been calculated by Dr. Backlund, of 

 Pulkowa ; and it is matter of regret to notice his ac- 

 companying announcement that this is the last occasion 

 on which he will be able to undertake it. The earlier 

 portion of this ephemeris was given in NatL'RE last 

 week. 



W. T. LvxN. 



PROGRESS OF THE CATARACT CONSTRUC- 

 TION COMPANY'S WORKS AT NIAGARA. 



'pHE general scheme of the Niagara Falls Power Com- 

 ■"■ pany has already been described in these columns 

 (N.ATURE, vol. xlix. p. 482). We understand that the 

 great power house is now complete, and the foundations 

 ready for the three great 5000-horse power dynamos 



NO. 1309, VOL. 51I 



which have been constructed by the Westinghouse 

 Company. The turbines and vertical shafts up to the 

 floor of the power house have long been in place, and the 

 dynamos may now be shipped any day. They have 

 already been revolved in the shops at full speed. Our 

 readers will remember that there is no gearing. The 

 dynamos are on a vertical shaft, and the revolving fields 

 are external to the armature, forming a sort of bell-cover 

 to it, with the poles pointing radially inwards. This was 

 the only design which Prof Forbes could make to fulfil 

 the requirements of the turbine designers as to maximum 

 weight and minimum fly-wheel effect to be allowed. It 

 gives a splendid mechanical construction, as the re- 

 volving pole-pieces and coils are retained in place against 

 the centrifugal forces by the nickel-steel ring which forms 

 the yoke. 



The first place to be supplied with current is the 

 aluminium works of the Pittsburg Reduction Company. 

 To convert the two-phase, 2000 volt alternating current 

 into a continuous current of 160 volts at these works. 

 2500 feet from the power house, transformers are there 

 used, and the low pressure alternating current in two 

 phases is supplied to commutating machmes. This is a 

 new departure of great interest, as no machines of this 

 class have been previously built except for experimental 

 purposes. They are each of 500-horse power, and are 

 continuous current machines with four rings attached to 

 four bars of the commutator. The alternating current is 

 supplied by brushes rubbing on these rings, and it drives 

 the machine as a motor. The continuous current is taken 

 from the commutator by brushes in the ordinary way. 

 All this machinery was made for the Cataract Con- 

 struction Company by the General Electric Company, 

 which is far the largest electrical concern in the United 

 States. The machinery was tried in September, and it 

 seems to work admirably. Four of these machines, with 

 eight transformers, equal to 2000-horse power, are being 

 put down to begin with. 



The next place to be supplied is the Carborundum 

 Company, which makes a substitute for emery, much 

 harder, being composed of carbon and silicon raised to a 

 high temperature in an electric furnace. They begin with 

 looo-horse power, and their factory is making good pro- 

 gress. 



After that the Buffalo transmission will go on, but the 

 selling of power in the neighbourhood is more profitable 

 than at a distance ; and many of the manufacturers, who 

 have been holding back for two years to see how the 

 tariff was to be settled, will now start factories, and 

 some of them will settle at Niagara Falls to get the 

 cheap power. 



The transformer house, for raising the electric pres- 

 sure from 2000 to 10,000 or 20,000 volts, is on the side of 

 the canal opposite the power house, and these are con- 

 nected by a massive stone bridge, with a covered way 

 for carrying the cables. The concrete subway starts from 

 the transformer house, and is at present to be used for 

 supplying the flrst customers on the Company's lands. 



Everything looks most promising at present, and 

 as to the electrical works, everything indicates that 

 any other general scheme than the one adopted 

 would have been vastly inferior. Especially is low 

 frequency proving itself invaluable. The continuous 

 current could not have been got for the aluminium works 

 without it, the motors will be far more satisfactory, and 

 the safety and economy of the line is far higher. It 

 was once objected that transformers could not be cheap 

 or efficient at the low frequency proposed. Prof. Forbes 

 held, however, that large sizes could be got even with 

 low frequency at half the cost and at higher efficiency 

 than anything that had been done on a small scale. 

 This statement was based upon his own designs ; and 

 now it is entirely supported by all the manufacturers 

 who have made designs for the work. 



