412 



NATURE 



[August 30, 19CX) 



press, is little more than a reprint of the first. But the 

 plates are a welcome addition. They represent seventy- 

 three species, without colour, carefully drawn and easily 

 recognisable, though sometimes badly printed. The 

 small size of the book renders it very convenient for 

 handy reference. A European entomologist will recog- 

 nise one or two old friends, such as the Camberwell 

 Beauty, the Painted Lady, Red Admiral, and a Small 

 Copper, hardly distinguishable from our own ; but the 

 proportions of the various families and genera are very 

 different from what obtains in Europe. A single plate, 

 representing five species, and another representing only 

 six species, are enough to illustrate the Satyridae, and 

 the Blues and Coppers together ; while a much more 

 crowded plate is required for the Hair-Streaks, and two 

 for the Skippers. There are also several very large and 

 conspicuous species, including six large Swallow-Tails, 

 and the northern representatives of several tropical 

 genera. But although the average size of the North 

 American butterflies is much larger than ours, and much 

 of the settled part of the country lies much further south, 

 the number of species in the Northern States is much 

 smaller than in Europe, owing to the comparative absence 

 of Satyridce and Lycasnidae ; and it is not till we reach 

 the frontiers of Mexico that the vast wealth of the tropical 

 American butterfly fauna (almost equalling that of all the 

 other continents put together) begins to dawn upon us. 



W. F. K. 



Elements of Qualitative Analysis. By G. H. Bailey, 

 D.Sc, Ph.D., and G. J. Fowler, M.Sc. Pp. 115. 

 (Manchester : J. E. Cornish, 1900.) 



Among the distinctive characteristics of this addition to 

 the already numerous volumes on practical chemistry 

 are : the prominence given to the recognition of common 

 elementary substances by an examination of their simple 

 physical and chemical properties, the attention given to 

 dry methods of analysis, and the series of flame-reactions. 

 These sections provide students of practical chemistry 

 with excellent exercises in manipulation, and will counter- 

 act the belief that the best way to analyse a substance 

 is always to dissolve it and go through the usual routine 

 treatment of solutions and precipitates. There is little 

 sympathy with ordinary qualitative analysis at the present 

 time, but where the subject is taught it should be taught 

 intelligently ; and as this little book provides a reasonable 

 course of laboratory work, it merits a trial. 



LETTERS TO THE EDITOR. 

 \The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undei'take 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or atiy other part of Nature. 

 No notice is taken of anonymous communications. '\ 



Railways and Moving Platforms. 



About twenty years ago I was in the habit of speaking with 

 Prof. Ayrton and other friends about a scheme which might 

 increase ten-fold the carrying capacity of the Underground Rail- 

 way. I prepared a letter for the Times newspaper about two 

 years ago, but at the earnest entreaty of a friend I applied for 

 patent protection for the scheme, and did not publish the letter. 

 I have not proceeded with the patent, and wish now that I had 

 published the letter. Indeed, I wish that, instead of merely 

 talking the matter over with friends twenty years ago, I had 

 published what I had to say. 



Travelling now on the new Central London Railway, one feels 

 that there is enormous waste of energy and of tinre in starting 

 and stopping the trains. Again, a train must not be longer than 

 the platform. On my scheme the train does not stop, and the 

 longer it is the better. Indeed, lean imagine an endless train 

 keeping a perfectly constant speed all the time. 



My scheme is easy enough to understand now that moving 

 platforms are common. After passengers enter a station I get 



NO. 1609, VOL. 62] 



them gradually into a state of motion, so that moving alongside 

 the train and at the same speed, they may enter and other 

 passengers may leave. There are many ways in which the 

 scheme may be carried out. From a wayside station passengers 

 may enter an express train which does not stop, in the following 

 way. They enter a small train at the station ; this train gradually 

 gets up a speed equal to that of the express ; it runs alongside 

 the express at a particularly well-laid part of the line ; there is 

 an exchange of passengers, and the local train gradually comes 

 to rest again at the station. 



For the Underground Railway, the method which most com- 

 mended itself to Prof. Ayrton and me long ago was this. At 

 a station, say St. James's Park, the platform was a carefully con- 

 structed turntable, 500 feet in diameter, the rim of which travelled 

 at 8 miles per hour. The whole area was not really a floor ; it 

 was only a skeleton of a turntable, being an outer rim 8 feet 

 broad and many radial passages. The very long train to Mansion 

 House, travelling at 8 miles per hour, was close to the rim of the 

 turntable; indeed geared with it in a rough, simple manner for less 

 than half its circumference ; the train from Mansion House did 

 the same on the other side. I need not speak of the automatic 

 opening and closing of the doors of the train. 



A passenger, let us say second class for Mansion House, takes 

 his ticket and descends a spiral staircase, which revolves so 

 slowly that even the frailest and most timid of old ladies is 

 not frightened ; in fact, it revolves on its own axis once in 134 

 seconds. At the bottom the passenger sees a few notices ; one 

 of them saying second class, Mansion House, has a hand 

 pointing along a radial passage, and this is followed. As 

 the passenger moves radially, he does not notice that he is 

 gradually getting up speed circumferentially. He does not 

 notice that the floor gets slightly inclined as he moves out, 

 to counteract the small effect of centrifugal force. When he 

 reaches the outside of the platform he probably finds a train 

 there, seemingly at rest, with the doors open, and he enters it, 

 moving perhaps along the platform, choosing one compartment 

 rather than another. If he is lucky he has about one minute in 

 which to make his choice. But he will notice near him on the 

 platform an altering time signal which tells him how much more 

 time he has to waste : 50 seconds, 40, or 30, or 20, or 10 ; if he 

 delays after the signal says o, an iron railing will come between 

 him and the train ; he will see the train moving laterally 

 away from the platform, and he must wait seventy-four seconds 

 before he sees a train coming laterally towards him; the 

 railing goes away, and he has again sixty seconds in which to 

 enter. 



If he had a third class ticket to South Kensington, he woukl 

 have proceeded in exactly the same way. Also every passenger 

 wanting to leave the train at St. James's Park had sixty seconds 

 in which to do it. Trains at 16 miles an hour give only 

 half these times. A platform of only 250 feet diameter would 

 give only half the time if the train speed was 8 miles an 

 hour. I need not dwell upon the details of this and other 

 methods which suggest themselves. It may be soon or syne, but 

 I feel sure — I have felt sure for many years — that my method 

 will have to be adopted. John Perry. 



August II. 



Snow-drifts on Ingleborough. 

 In his interesting letter on "Snow-drifts on Ingleborough in 

 July," Prof. Hughes describes what may be called the first stage 

 in the formation of a glaciere. These ice-caves, not very rare in 

 parts of the Alps and Jura, were made by the present Bishop of 

 Bristol the subject of an attractive book (published thirty- five 

 years ago), and have been occasionally noticed in the earlier 

 volumes of Nature and elsewhere. I have always beheved 

 that snow, drifted into caves during the winter, was the initial 

 cause of these natural ice-houses (about half a dozen of which I 

 have visited), and can quote a case from the Alps which is a 

 slight variation of that described by Prof. Hughes. On July 24, 

 1873, I went up the Pic d'Arzinol (9845 feet) from Evolena in 

 the Val d' Kerens, and on the way down — so far as I remember 

 between five and six thousand feet above sea-level — my guide 

 diverged from the track to show me what he called the Pertuis 

 Freiss. These were two fissures, apparently joints, opened by a 

 slight subsidence. A description of one will serve for both, 

 except that there was hardly any descent to its floor. The fissure 

 extended some four yards into the hill, and was at widest about 

 as many feet. Ice was patched about the floor, and in places 



