8 



NATURE 



[November 6, 1902 



completely. It is rather hard for the " explanation " of 

 magnetism. 



The kinetic energy of molecules is the natural source of the 

 radiation, but the connection between them and the electrifica- 

 tion is very obscure, and how the electrons get knocked off is 

 harder still, and what they are is hardest of all. Larmor thinks 

 they run through the ether like knots on a string. If they do, 

 as they may, how do they do it ? Connections are warned. 



Oliver Heaviside. 



Leonid Meteors, 1902. A Forecast. 



The historical interest which attaches to the Leonid star 

 showers naturally renders the near approach of mid-November 

 a subject of paramount importance to meteor observers. Nor is 

 expectation lessened on the present occasion by the moderate 

 though somewhat unexpected brilliance of the Leonid display 

 witnessed last year in America on the morning of November 15. 

 The question must naturally occur to many, will there be a 

 revival of the phenomenon in the November of 1902, and if so, 

 will it make its appearance in a less or a more intensified 

 form than in the previous year ? Generally speaking, the 

 prospects of a star shower on the night of November 15 

 this year are very good. An analysis made by the writer of 

 the conditions under which last year's shower appeared, and 

 also of those connected with the more brilliant meteoric 

 spectacles of the past, shows that the event of November 15, 

 1901 , is likely to be much surpassed by the meteoric phenomenon 

 of 1902. The display falls due on the night of November 15 

 on the present occasion, and not on that of November 14 as was 

 the case last year and was duly predicted by the writer {Daily 

 Chronicle, November 14), though the maximum occurred some- 

 what later on that night than had been expected. The first 

 phase of the shower will take place, however, at an hour not 

 very well suited for its observation in western Europe, the time 

 of its maximum being November 15c!. ioh. 45m. G.M.T., 

 when the radiant will be not much more than just above the 

 horizon. Meteors from a radiant in full activity as it emerges 

 above the horizon afford an interesting spectacle, however, and 

 though their numbers must in consequence be seriously 

 diminished, they somewhat atone for their paucity by often long 

 and rapid flights across the heavens. This first appearance of 

 the shower will of course be best observed in places situated at 

 least a few hours to the east of Greenwich, though it ought not 

 to escape observation in our less favoured localities. This early 

 display promises to vie in brilliancy with that observed on the 

 western slopes of the Pacific in 1901, if atmospheric conditions 

 turn out favourable in those places best suited for its observation 

 on the night of November 15, and in all places where the 

 radiant will be above the horizon at the time of its maximum it 

 ought to render shooting stars pretty abundant during the early 

 hours of that night. 



The second maximum of the Leonid display has been calcu- 

 lated to take place on November 1 5<d. iSh. 45m., and promises 

 to be the richest display of the night, though the time of its 

 highest brilliancy will scarcely enable observers to obtain the 

 most satisfactory view of it on this side of the Atlantic, as the 

 increasing twilight between six and seven o'clock in the morning 

 must somewhat impede observation. Along the eastern coast of 

 America, on the other hand, the shower is likely to prove an 

 attractive spectacle to observers, and its full strength can better 

 and more accurately be subjected to calculation than with us, as 

 its maximum will occur there at about two o'clock (local time) on 

 the morning of November 16. Though that hour is rather early 

 for its best observation, as the Leonid radiant is most favourably 

 situated for purposes of meteoric observation in any place at 

 about 4 o'clock in the morning (local time), yet on the present 

 occasion at no other place can a better and more systematic 

 watch be maintained for the anticipated star shower than along 

 the Atlantic side of the American continent. Passengers on 

 vessels crossing the Atlantic will no doubt find themselves 

 specially favoured with opportunities for observing the pheno- 

 menon, as has been the case in previous star showers, such as 

 that of 186S. The calculations made with respect to this meteor 

 display go to prove that it will decline rather rapidly after 

 i8h. 45m. on the night of November 15, the maximum showing 

 a tendency to occur rather before th n after the time indicated, 

 and on this account shooting stars are very likely to appear in 

 unusual numbers to European observers throughout the night in 

 question. As has been already stated, the shower expected in 



NO. 1723, VOL. 67] 



the present year gives considerable promise of surpassing in 

 intensity that of 1901. Indeed, the calculated strength of the 

 former is from ten to fifteen times that of the latter, but the 

 presence of a full moon throughout the night of November 15 

 has not been taken into account in the determination of the 

 foregoing comparison, and this circumstance must detract con- 

 siderably from the relative splendour of the meteoric epoch of 

 the present year. The full moon will probably obliterate the 

 close of this year's shower, the end of which has been timed to 

 take place on November i6d. 2h. 30m., and is generally of too 

 weak a character to require any special consideration. It may be 

 added that the foregoing calculations have been based on the 

 assumption that the maximum of the Leonid shower of 1866 

 occurred at ih. 15m. on the morning of November 14, G.M.T. 



John R. Henry. 

 20 Rathmines Road, Dublin, November 3. 



Curvature of Wheel Spokes in Photographs. 

 Many people must have noticed the curious curved appear- 

 ance presented in a photograph by the spokes of a moving 

 vehicle. It is well known that the envelope of a diameter of a 

 circle rolling along a straight line is a cycloid of half the dimen- 

 sions of the cycloid traced by a p^int on the circumference. 

 The part of the moving spoke which makes the strongest 

 impression on the photographic plate will be where it intersects 

 the consecutive position, so that the photograph really gives us 



a small piece of the envelope of each spoke. The effect may be 

 compared to the ordinary caustics of reflection or refraction. 

 The accompanying photograph shows, not only the curvature of 

 the spokes, but also the cusps of the envelopes of the spokes the 

 ends of which have touched the ground during the exposure. In 

 the diagram, the envelopes for a circle with fourteen equidistant 

 diameters are drawn, and the parts of the envelopes which have 



been put in strongly indicate the appearance that would be 

 presented in a photograph, supposing that three spokes had 

 touched the ground during the exposure. The spokes on the 

 upper half of the moving wheel leave no impression on the 

 plate, because their points of ultimate intersection lie outside 

 the spokes themselves. R. M. Milne. 



Royal Military Academy, Woolwich, S.E. 



The Turkestan Earthquake of August 22. 



Information received in India leaves no room for doubt 

 that the eaithquakeof August 22, which left such conspicuous 

 traces on the seismographs of Europe, had its origin in Central 

 Asia. The representative of the Indian Government at Kashgar 

 reports that there was a severe earthquake there at 8 a.m. on 

 August 22, which lasted one-and-half minutes. Repeated 



