November 1, 1897.] 



KNOWLEDGE. 



249 





LONDON: NOVEMBER 1, 1897. 



CONTENTS. 



By W. F. 



The Approaching Shower of Leonids. 



Denning, F. It. A. 8 ■•• 



The British Trapdoor Spider. By Feed. Enock, l.L.ta., 



F.K.S. {Illustrated) 



The Mystic Number Three 



Photography in Illustration. By H. Snowden Waed, 



F.K.P.8. 



The Flight of a Seed. By Eer. Albx. S. Wilson, M.A., 



B.So. (Illuxiraled) ... ' 



British Ornithological Notes. Conducted by Haeet F. 



WlTHEEliT, F.Z.S., M.B.O.U 



Some New Views as to the Planet Venus.— II. By 



C'AMILLK Flammarion, F.E.AS. (Illustrated)... 



Photograph of the Moon. (Plate) 



Letters: — Lionel Jkrvis; Chaeles A. Witchell; Regi- 

 nald Bainbeidge; T.Wilson 

 Science Notes (I I In. s (rated) ... 

 English Plains and Escarpments. 



B.A.Cantab., F.R.S 



Literary Supplement— 



The Stitdt and Use of Scientific Liteeature By 

 R. Lydbkker 



Reviews (III h.sI rated) 

 The Language of Shakespeare's Greenwood — III. By 



GeciRGE IIOELEV 



Egg Collecting in its Relation to Science. By Leopold 

 Field, F.R.A.S 



The New State Laboratory (Illustrated) 



The Face of the Sky for November. By Herbert 

 Sadlee, F.R.A.S. 



Chess Column. By C. S. Looock, B.A.Oxon 



249 



250 



252 



253 



254 



256 



258 

 261 



261 

 258 and 263 



By E. Lydekkee, 



263 



273 

 274 



265 



266 

 268 



271 

 271 



THE APPROACHING SHOWER OF LEONIDS. 



By W. F. Denning, F.E.A.S. 



THE return of the autumn season, and of that 

 significant epoch at the middle of November which i 

 has furnished some of the most brilliant and 

 abundant star-showers on record, will naturally 

 draw a large amount of attention to the phenomena 

 of meteors, and especially to the circumstances affecting the 

 ensuing return of the Leonids. Only seen in their most 

 striking characters at intervals of a generation, it is need- 

 less to say that observers are awaiting their reappearance 

 with keen interest, and in full expectancy of witnessing a 

 spectacle sufficiently impressive to form a thrilling expe- 

 rience and a lifelong remembrance. 



Brilliant showers of Leonids occurred in 1790, 1833, 

 1866, 1867, and 1868, and it is fair to assume that the 

 years 1899, 1900, and 1901 will be similarly favoured. 

 The revolution of the swarm round the sun is accomplished 

 in as nearly as possible thirty-three and a third years, so 

 that, since the earliest recorded manifestation of the 

 shower, its displays have recurred in the same years of 

 the century, though the variable conditions of weather, 

 moonlight, and time of rencontre of the earth with the 

 densest region of the stream, have affected the character of 

 the exhibitions, and in certain years enabled them to escape 

 detection altogether. There were displays in 902, 1002, 

 1202, and 1602 ; also in 1366 and 1866. Others were 

 seen in 931 and 934, to be repeated in 1533 and 1833. 



During the next seven or eight years, the middle of 

 November will be sure to furnish an abundance of Leonids, 

 with a maximum either in 1899 or 1900. In 1897 the 

 conditions are not promising as regards a really brilliant 

 return. At the important time the moon will be only a 

 few days past the full, and visible all the time that the 

 Leonid radiant will be above the horizon. In addition to 

 this, it must be remembered that the perihelion passage of 

 Tempel's comet (1866 I.), from which the meteors are 

 derived, and near which they are apparently clustered in 

 their greatest abundance, is not due to return until the 

 spring of 1899, so that the earth will cross the orbit far 

 in front of the comet. In fact, the latter must run its 

 course during another one and a half years before it reaches 

 that point of its orbit which will be nearly intersected by the 

 earth in November, 1897. 



Is it likely, therefore, that, at a section of the stream 

 vastly distant on the preceding side of the derivative comet, 

 the meteoric particles are distributed in sufficient numbers 

 to form a numerous display '? The answer must be in the 

 affirmative if we are to judge from previous experiences, for 

 it is certain that a host of meteors are in the van as well 

 as the rear of the comet. Tolerably brilliant displays 

 occurred in 1831 and 1864, which nearly correspond with 

 1897 as regards relative positions of the earth and comet, 

 though in the latter year the conditions are not quite so 

 favourable as in the former. 



It may be interesting to make some brief quotations 

 from the observations in 1831 and 1864, as the return of 

 the present year appears likely to form a parallel. Captain 

 Bcrard, of the French brig f.niret, then oft' the coast of 

 Spain, near Carthagena, reported to M. Arago as follows ; 

 "The 13th of November, 1831, at four o'clock in the 

 morning, the sky being perfectly cloudless and a copious 

 dew falling, we saw a number of shooting stars and luminous 

 meteors of great dimensions. During upwards of three 

 hours more than two per minute were seen." Dr. Wright, 

 of Ohio, U.S.A., also observed a shower of shooting stars 

 on the night following November 12th, 1831. In 1864, on 

 the morning of November 13th, " a grand display of 

 meteors " was observed from the steamship Ellnrn, oft' 

 Malta. " The watch— an old sailor and an intelligent 

 man — said it was the grandest display he had ever seen, 

 and that the whole watch had been looking at them with 

 delight." 



These descriptions justify the inference that many 

 meteors will be seen on the morning of November 14th 

 next. It is true, however, that the forerunners of the dense 

 part of the stream which furnished displays in 1833 and 

 1866 will envelop the earth for a few hours at about noon 

 on November 14th, and will, therefore, be visible neither in 

 England or America. But immediately outlying the central 

 group, on each side, there appear to be other clusters 

 capable of yielding rich displays, and something of these 

 should be observed both on the mornings of November 

 14th and 15th. It must be admitted, however, that the 

 past history of the visible appearances of the shower, and 

 of the meteorological and other conditions affecting them, 

 are insulticiently known to warrant any definite conclusion 

 as to the actual strength of the display which will be 

 manifested this year. But as two meteors per minute 

 were counted in 1831, and as " a grand display " was seen 

 in 1864, notwithstanding the presence of a full moon, we 

 may reasonably expect that after the radiant point has 

 reached a fair altitude, at least one meteor per minute 

 wOl be visible. In fact, the Leonid shower of 1897 ought 

 to quite equal, if not surpass, a rich return of the Perseids 

 of August. 



The sky will be light, for the gibbous moon will be 



