November 22, 1900J 



NATURE 



'^Z 



eye, their retinal images must be separated by at least one 

 unexcited retinal cone. The distance between the two images 

 roust therefore be "004 mm., or the intervening cone may be 

 encroached upon. Therefore the minimum visual angle 



fl = 20 = S3"236". 



Now Jupiter's edge and his first satellite may subtend at the 

 sun an angle of 1*33", so that we may regard this as the 

 average angle subtended at the earth. Hence we see that there 

 is no optical reason why the four satellites should not be seen 

 by the naked eye. If they were sufficiently bright they no 

 doubt could be distinguished by the normal Englishman's eye. 

 " It must be remembered, however," as Sir Michael Foster 

 says, " that the fusion or distinction of sensations is ultimately 

 determined by the brain. The retinal area must be carefully 

 distinguished from the sensational unit, for the sensation is a 

 process whose arena stretches from the retina to certain parts of 

 the brain, and the circumscription of the sensational unit, 

 though it must begin as a retinal area, must also be continued 

 as a cerebral area, the latter corresponding to, and being, as it 

 were, the projection of the former." No amount of education 

 can make the sensational unit smaller than the minimum retinal 

 area, though by practice the cerebral area may be made more 

 sensitive to minute sensational impulses. 



A. S. Percival. 



26 Ellison Place, Newcastle-upon-Tyne. 



ELECTRIC TRACTION TROUBLES. 



THE English — the pioneers in the development of 

 railways, steamships, the telegraph, and other 

 inventions of the nineteenth century — are now running 

 the risk of becoming a nation of imitators. Apart from 

 the fact that the entire route, Shepherd's Bush to the 

 Bank, was not sent bodily across the Atlantic to be 

 tunnelled, the Central London Railway might almost as 

 well have been constructed in Central America as in 

 Central London. 



For not merely did the steam-engines come from 

 Milwaukee, the electric lifts from New York, the dyna- 

 mos, locomotives, and other electric apparatus from 

 Schenectady, but the curious practice of requiring a 

 passenger to first purchase a ticket and then drop it 

 immediately into a box, as well as the projection of 

 information into each end of a car on quitting each 

 station are Yankee notions, and one expects to hear that 

 the "next station is Chippawa" or Winettea, and not 

 commonplace Bond Street or Oxford Circus. 



The characteristics of American traction are, conveni- 

 ence, comfort, speed, low fares and a liberal scattering 

 of the electric current over the district generally. Chinese 

 like, we have faithfully adopted them all. To go from 

 the City to the Albert Hall, up to this summer, one went, 

 of course, from the Mansion House to the South Ken- 

 sington railway stations. Now one saves time and money 

 by being whisked electrically to Lancaster Gate and 

 walking across Kensington Gardens. No wonder, then, 

 on C.LV. Monday 230,000 people used the Central Lon- 

 don Railway, enough passengers, in fact, to fill every seat 

 one and a quarter times in every train from early morn 

 on Monday to the small hours of the following day. 



No need to issue return tickets at reduced rates when 

 every passenger who goes by this line can be relied upon 

 to return by it. What matters it, then — may think the 

 artisan, the clerk, the stockbroker, the investor, and even, 

 perhaps, the engineers and directors of the Central 

 London Railway itself — by what route the electric cur- 

 rent returns ? The electric current that starts from the 

 Marble Arch, say, must, from the nature of things, go 

 back there. Why, then, should advantages be ofifered it 

 that are not thought necessary in the case of the general 

 public to induce a return home inside the tube ? 



If one were a shareholder only of the Central London 

 Railway, one might find it difficult to realise that any 



NO. 1 62 I, VOL. 63] 



other interest was of any consequence. But, if a con- 

 siderable portion of one's income happens to be derived 

 from dividends on the shares in gas and water com- 

 panies, one may prefer that these sources of income shall 

 not be seriously interfered with. Hence, the clean white 

 glazed brick walls, the brilliant arc lamps, the pleasant 

 gliding lifts, the entire absence of those rolling clouds of 

 smoky steam that greet a passenger as he descends into the 

 Euston Road on a damp, cold November day, fail to cheer 

 him on his swift modern progress under Oxford Street, 

 should he make the following little elementary calcula- 

 tions : — Over 2000 electric horse-power which, at times, 

 every day is already actually put into the Central London 

 Railway at a single sub-station between Shepherd's Bush 

 and the Bank means a current of over 3000 amperes ; and 

 this current, after passing through the electro-motors on 

 the trains in the neighbourhood of that sub-station, has 

 to come back there through the uninsulated rails on 

 which the trains run. Suppose, in consequence of these 

 rails being ««insulated, 10 per cent, of this return current 

 strays outside the iron tube and comes back by the iron 

 gas and water pipes running parallel with the railway on 

 the ground above it. This means about Jib. of iron 

 removed from the gas and water pipes in an hour in the 

 neighbourhood of a sub-station. 



Such large currents, however, as 3000 amperes are at 

 present probably only seldom reached, therefore, to avoid 

 even an approach to exaggeration, let us assume that the 

 average current which strays into the gas and water 

 pipes on its way back to a sub-station is only, say, 

 x^Jg^th of the maximum value of the current leaving a 

 sub-station each day. This seems a modest enough 

 estimate. Then, since the line works some eighteen or 

 more hours per day, this means about a quarter of a ion 

 of iron removed per year from the gas and water pipes 

 in the neighbourhood oi each of the places at which the 

 current is fed into the railway. Consequently, as there 

 are several such places between Shepherd's Bush and 

 the Bank, this would lead to more than one ton of iron 

 being eaten out of the pipes each year. 



Is this important ? Well, as holders of gas and water 

 companies shares we should say, very ! But are the 

 traveUing facilities of the London public to be interfered 

 with, is the development of electric traction to be ham- 

 pered — ^just when our people are having their first taste 

 of the immense advantages that accrue from propelling 

 trains and tramcars by electricity — simply because several 

 millions sterling happen to have been invested on pipes, 

 retorts, gasometers, waterworks, &c , and because there 

 are people so blind as to actually prefer the receipts of 

 regular dividends to the slavish copy of American 

 practice ? 



Luckily, no such terrible alternative need be flourished 

 in the faces of our democratic governing bodies, who, 

 while naturally anxious to defend the people from the 

 supposed extortions of the gas and water companies, are 

 no less anxious to shield from the incursions of the 

 electric traction capitalist a large class of persons with 

 small incomes who have placed their savings in what 

 they rightly regarded as safe investments — viz., the shares 

 of gas companies. 



Another electric service has been inaugurated this year 

 in which trains as large as, or larger than, those on the 

 Central London Railway are driven electrically over a 

 far more difficult route — viz., from Earl's Court to High 

 Street, Kensington, among ordinary trains over points 

 and crossings. 



And yet, in spite of this greater difficulty, there is not 

 merely an insulated conductor to take the electric current 

 to the trains, as on the Central London Railway, but 

 also an insulated conductor to bring it back by ; and the 

 rails on which the electric trains run between Earl's 

 Court and High Street, Kensington, are used simply for 



