August 29, 1901] 



NA TURE 



437 



amount of light all over the plate. The total brightness of the 

 corona will thus depend on the area of sky included. Assuming 

 this to be a circular area 5° in diameter, the total brightness 

 of the 1898 corona would be about 2'4 times that of full moon, 

 while the 1893 corona was only about fl times brighter than 

 the full moon. 



The Spectroscopic Binary "Mizar." — During March 

 and April of the present year a series of excellent photographs 

 of the spectrum of this star, C, Ursa* Majoris, were obtained with 

 Spectrograph IV. and the t,}, cm. refractor at the Potsdam 

 Observatory. Dr. H. C. Vogel has measured these, and gives 

 the result of the reductions in the Astrophysical Journal (vol. 

 xiii. pp. 324-328). On some of the plates as many as sixty-five 

 lines are recognisable, including several of the strongest iron 

 lines and lines of silicon and magnesium. When the period of 

 maximum separation occurs, however, many of these become 

 faint and the measures are more difficult. 



On several of the plates the separated magnesium lines at 

 A44S1 appeared of unequal width, but no change in their be- 

 haviour was discernible after a coincidence. 



The values of the relative motion are given for twenty-five 

 plates obtained during the period igoi March 24-May I, ranging 

 from 1 58 to 15 kilometres per second. 



The motion of the whole system is given as 16 km. per 

 second. A diagram is given showing the velocity curve most 

 nearly representing the final reduced measures, and the period 

 thus deduced is 20 '6 days — considerably less than the period of 

 104 days deduced by Pickering about 1S90. 



The following provisional elements have been computed from 

 the curve by Lehman-Filhes' method on the assumed values of 



Period = 20 '6 days. 

 Maximum relative velocity of A = 128 km. 

 „ B = 156 ,, 



To = 1901 March 28 '60 (Rel. motion in line of sight = o). 

 T =1901 March 28-88. 



oi = ioi°'3. 



e = 0-502. 

 logM = 9 •4843- 

 M = I7°476. 

 a sin z = 35 million kilometres. 

 40 

 ' sin-*/. 



Nova Persei. — In the Aslrophysical Journal (vol. xiii. 

 pp. 336-7) Messrs. G. C. Comstock and J. Stebbins give a very 

 exhaustive series of comparisons of the estimated brightness of 

 Nova Persei from February 24 to May 12. The observations 

 were made by the "grade" method of Argelander, the esti- 

 mated error being O'l magnitude for a single comparison. The 

 rapid variation of the star is well shown by the many cases 

 where several observations were obtained during the same 

 evening. The minimum magnitude recorded is 5 '7* Most of 

 the estimates were made with the help of an opera-glass, the 

 comparison stars being those given on Hagen's special chart 

 of the region. 



THE FUTURE OF ELECTRIC TRACTIONS 



TT is not so long since the Englishman, and perhaps more 

 ■*• particularly the Londoner, first tasted the sweets of electric 

 traction, but he has already found it so satisfactory, whether as a 

 profitable investment or as a method of travelling at once com- 

 fortable, convenient and healthy, that he is clamouring for its 

 rapid extension and development. It is beginning to be realised, 

 too, that electricity as a motive power is not destined to be con- 

 fined to metropolitan railways and suburban tramways. The 

 electrification of our larger railways is now being discussed as a 

 practical problem by the more far-sighted of our engineers, who 

 have recognised that many of the railway systems characteristic 

 of this country are peculiarly suited for electrical running. Mr. 

 Langdon, now president of the Institution of Electrical Engineers, 

 devoted a paper read last November before that society to the 

 subject ; and Major P. Cardew, in his recently delivered Cantor 

 Lectures, again gave prominence to the question. 



1 " On the Supersession of the Steam by the Electric Locomotive." By 

 W. Langdon. ijoitmal of the Institution of Electrical Engineers, vol. 

 .\.\x. p. 124.) 



■■ Electric Traction." By Major P. Cardew. Cantor Lectures. (Journal 

 of the Society of Arts, July 12,19 and 26.) 



It is intereslingto consider what are the conditions of working 

 which would make a railway one in which the adoption of 

 electric traction is likely to prove profitable, for unless the 

 alteration results in the increased economy of the system it is 

 clear that it is not likely to be made. " Electric traction," says 

 Major Cardew, "tends towards the ideal of the continuously 

 moving platform," and one may say that the more nearly a 

 railway tends towards the same ideal the more likely is the 

 adoption of electricity as its motive power. In those most 

 closely approaching this limit, namely, the metropolitan railways, 

 all other systems at present known have long been seen (by all 

 except perhaps the directors of the London underground and 

 district railways) to be doomed. Tne reason lies in the essen- 

 tial difference between steam and electric driving, namely, that 

 in the one case the train must carry its own power generator 

 whilst in the other the power is generated in bulk for a number 

 of trains. Since the generation of power in bulk is much 

 cheaper than in detail, the tendency with steam locomotives is 

 to make each detail as large as possible, and therefore to run 

 heavy trains at long intervals. With electric working, on the 

 other hand, it is desirable to make the load on the generating 

 station as constant as possible, which can only be done when the 

 number of trains is large and each only takes a small fraction of 

 the total load ; for in such a case the stopping and starting of 

 individual trains will only have a small percentage effect on the 

 output of power. It will readily be seen, therefore, that for 

 long-distance traffic the steam locomotive is likely for some time 

 to come to hold its own, for here the number of passengers is 

 not so great as to be able to support a very frequent service of 

 light trains, and, moreover, the time taken over the journey, 

 being nearly the whole of the day or night, practically fixes the 

 starting times. With lines communicating between important 

 towns not too far apart (about too miles is the limit given by 

 Major Cardew), electric traction could be introduced with 

 advantage ; in this case a frequent service of light trains would 

 be a great benefit, especially if a number of important centres 

 lie on the route between the termini and if there is a field for 

 metropolitan traffic at the ends of the line. In such lines our 

 small but densely populated country abounds. 



Many additional advantages are introduced at the same time 

 as the principal gain in the lessening of the cost of power 

 generation. Thus the driving power can be distributed throughout 

 the train, which results in les.sening the wear of the permanent 

 way and also in a lessening of the slip of driving wheels, as a 

 greater proportion of the weight of the train is used for adhesion. 

 It is easier, too, to provide power for accelerating the train and for 

 mounting gradients, as the extra power needed in these cases 

 is derived from an outside source, whereas if a steam engine 

 were made powerful enough for very quick acceleration it would 

 be too powerful for economical working during the greater por- 

 tion of its running time. The concentration of power genera^ 

 tion at a few centres leads to many economies in working 

 expenses ; coal and water are only used at the generating 

 station, and it is only there in consequence that means for their 

 storage and handling have to be provided. 



Those who are more keenly interested in this question will do 

 well to read the paper by Mr. Langdon to which reference has- 

 been made above. They will there find the matter thrashed 

 out in considerable detail, both in the paper itself and in the dis- 

 cussion upon it, with the estimated saving worked out from a 

 consideration of the existing traffic over a section of the Mid- 

 land Railway, fifty miles long, between London and Bedford. 

 Major Cardew discusses the problem more generally, but in his 

 third lecture enters with some detail into the equipment of an 

 imaginary typical full-scale railway fifty miles long ; for this he 

 arranges a suitable time schedule and then estimates the amount 

 of power required and the approximate cost of equipment. 



^lajor Cardew equips his imaginary railway on the polyphase 

 system, which he considers, on account of "the advantages 

 obtained in regard to means of conversion and from the use of 

 higher pressure," to be most suited for use on full-scale railways. 

 Space does not permit us to enter into a discussion of the relative 

 merits of three-phase and direct-current working, and we must 

 content ourselves with referring the interested reader to Major 

 Cardew's lectures, where he will find the question fully con- 

 sidered. Here, in England, we are not very familiar with 

 polyphase currents, but on the Continent, and in Switzerland 

 espectally, there are many railways thus equipped, and there 

 can be no question of the willingness of Continental engineers 

 to introduce their wares into this country if, as is to be feared, 



NO. I 66 I, VOL. 64] 



