542 



NATURE ^ 



[October 8, 189: 



dilating the height of that. I made several observations of the 

 position of the ceBtral line of the arch. I might specify that at 

 9.25 it was at R. A. 2oh. 42m., Decl. + 33|°,and R,A. oh. 43m,, 

 Decl. + 33°, nnd it iiioved very slowly. 



Is it not time some s)stcmatic efibrt was made to calculate 

 the heights of auroras? A good many observations have been 

 made on this point, showing great variation in height ; and yet, 

 beyond the conclusion that it seems probable they may be seen 

 at lower elevations nearer the magnetic pole than elsewhere, we 

 l<now nothing as to whether ihey vary in height with the place, 

 the time, or the nature of the auroras. Now is the time, seeing 

 that auroras appear to be becoming more numerous than they 

 have been for many yecrs past. T. W. Backhouse. 



West Hendon House, Sunderland, October 5. 



T' 



SOME NOTES ON THE FRANKFORT INTER- 

 NA TIONAL ELECTRICAL EXHIBITIONS 



III. 

 From Ore Hundred to Tiventy Thousand Volts. 

 HE incandescent lamp having, by 1885, reached a 

 fair degree of perfection, it appeared that the one 

 need still remaining, in connection with the distribution 

 of the electric light over a large area, would be supplied 

 by the use of transformer?. For a transformer with many 

 convolutions of fine insulated wire on one coil, and a few 

 convolutions of thick insulated wire on the other, would 

 transform a large pressure and small current into a small 

 pressure and large current ; hence, if such a transformer 

 were placed in each house, it would be possible to light 

 up even a scattered district by a comparatively fine wire 

 from a central station, whereas previously it had seemed 



on or off. There are, of course, two conditions to be ful- 

 filled in electric lighting : one, that turning on or off 

 lamps in one house shall not affect the brightness of the 

 lamps in any other house ; the other, that turning on or 

 off lamps in one room shall not affect the brightness of the 

 lamps in any other room of the same house. With trans- 

 formers in series, the first condition is satisfied by keeping 

 thealternating current which passes through the fine wire or 

 primary coil o{\\it. transformer perfectly constant ; but this 

 does not render the potential difference between the wires 

 from the secondary circuit, or house mains, independent of 

 the current in this secondary circuit— that is, independent 

 of the number of lamps turned on in the house. Conse- 

 quently, the series arrangement of transformers adopted 

 by Messrs. Gaulard and Gibbs, while rendering the lamps 

 in one house independent of those in another, did not 

 attain the same result for lamps in different rooms of the 

 same house. 



Complaints, therefore, became general. Various un- 

 successful devices were tried to remedy this evil, when an 

 application was received from Mr. Sebastian Ziani de 

 Ferranti to be allowed to try a transformer which he had 

 designed. The application was accepted, for Mr. Ferranti, 

 although quite young, was already known as having con- 

 structed an ingenious alternate-current dynamo, and in 

 February 1886 the charge of the Grosvenor Gallery 

 central station passed over into Mr. Ferranti's hands. 



The new engineer recommended that the system of 

 placing the transformers in series should be totally dis- 

 carded, and that a parallel arrangement should be adopted 



that it would be necessary to use copper conductors many 

 square inches in cross-section to light many houses even 

 when at no great distance from one another. 



Hence, in the autumn of 1S85 %ve find Messrs. Gaulard 

 and Gibbs making preparations at the Grosvenor Gallery, 

 Bond Street, for establishing there the pione^ central 

 station for London. 



But the method they adopted was that of placing the 

 transformers in series, as seen in Fig. 2, and this system 

 has the great disadvantage that the brightness of the 

 electric lamps in a house cannot be kept automatically 

 constant when other lamps in the, same house are turned 



' Continued from r, 524.. 



NO I 145, VOL. 44] 



in its place, as in Fig. 3, because a well-made transformer 

 had this important property —that if the potential differ- 

 ence at the terminals of the primary coil were kept con- 

 stant, the potential difference between the terminals of 

 the secondary coil would also remain nearly constant 

 whatever were the current passing through this circuit ; 

 so that if the pressure between the street mains were 

 always kept the same, the brightness of the lamps would, 

 hardly be affected either by turning on or off lamps in 

 the same or in any other house. 



Placing the transformers in parallel, however, would 

 necessitate working at a low pressure, said the press, and 

 would rob the transformer system of all its value, for " it 

 is surely not proposed for one moinent to work a parallel 

 system where the priinary has a difference of potential of 

 2000 volts." However, that is exactly what Mr. Ferranti 

 not only proposed to do, but what he actually carried out 

 on a large scale, so that his mains by 1888 stretched from 

 Regent's Park to the Thames, and from Chancery Lane to 

 Hyde Park, supplying current to some 20,000 glow-lamps. 

 The Board of Trade had made regulations, about 200 

 volts being the maximum pressure permitted in a house ; 

 Parliament had passed the Electric Lighting Act of 1882, 

 containing clauses rendering the development of the. 

 electric lighting industry well nigh commercially im- 

 possible ; but Mr. Ferranti ov^ercaine all these legalities by 

 laridging his mains from house-top to house-top, instead 



