262 



KNOWLEDGE. 



[November 1, 1898. 



brought about the separation of sexes in the prothalli, or if 

 the acquirement of dirooious conditions in the oophyte 

 stage was followed by modification of the spores. That the 

 establishment of the heterosporous condition dates far back 

 in the world's history is proved by the fossils of our coal- 

 fields, which show that it existed in some of the great tree- 

 like ancestors of Selaginella and its allies, which ilourished 

 in the swamps round the Carboniferous seas. 



All we can pretend to show in this sketch is that this 

 little mountain " moss," so much less conspicuous than 

 its cousins the ferns, yet contains, for those who care to 

 look at it, the evidence of a great change in organic 

 evolution, which has modified the whole course of plant 

 development, and made our trees and flowers what they 

 are to-day. 



It is possible that among the upland districts that form 

 the home of the little Selaginella we may find a better 

 known and more conspicuous member of the plant-world 

 to supply the next link in the chain. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.r.a.s. 



Comet Peerine-Chofardet. — This comet was discovered 

 on September 13th by Perrine, and on the following night 

 by Chofardet. It was visible in the morning sky, and 

 situated a few degrees north of the "sickle" of Leo. 

 Moving rather quickly to the south-east, in the direction 

 of the sun, it was increasing in brilliancy, but assuming a 

 position much less favourable for its observation. It came 

 to perihelion on October 20th, and in November its motion 

 will have carried it so far into the southern sky that it will 

 cease to be visible in our latitude. The following is from 

 an ephemeris by Berberich (Ast. Nach. 8520). 



Distance in 

 Date. E.A. Declination. miDions of Bright- 



1898. h. m. c ' miles. ness. 



October 18 13 29-8 - 6 10 128 8-7 



November 3 15 25-9 27 44 131 40 



lit 17 27-0 38 42 145 1-8 



December 5 19 12-5 -40 36 170 05 



Wolf's Cojiet is moving slowly to the south-west in 

 Monoceros, but it is a faint object even in powerful tele- 

 scopes. 



The Expected Shower of Leonid Meteors. — The 

 absence of moonlight at the middle of November is a 

 highly favourable circumstance, and a pretty abimdant 

 display of meteors should be observed if the weather is 

 clear on the morning of November 15th. In 1832-, Novem- 

 ber 12th, Dawes observed " most astonishingly brilliant 

 meteors from the east, with little intermission for about 

 an hour, when a thick fog supervened." In 18G5 many 

 meteors were seen at Greenwich and other places, but the 

 shower could not rank as one of first-class importance. 

 Though 1899 and 1900 will furnish the richest displays, 

 there will be many of these objects seen in the present 

 month. Observations should not be commenced before 

 11 p.m., as the radiant will not rise until shortly before 

 that hour, and the most brilhant exhibition of meteors will 

 probably occur in the early hours of the 15th. But a 

 look out should be maintained also on the mornings of 

 November 14th and IGth, especially by those observers 

 who wish to study the scientific aspects of the phenomenon. 

 There will probably be more Leonids seen than Perseids 

 in a pretty active return of the August stream ; but we are 

 scarcely justified in assuming that the shower will furnish 

 its thousands of meteors as it did in 1833 and 1806, for 

 the earth traverses the orbit at a point considerably in 



front of the parent comet, and we know that the most 

 profuse distribution of its material lies on the following or 

 rear side of the comet. Those who watch the ensuing 

 return of the meteors will do well to trace them on several 

 nights and to accurately determine their radiant point, 

 horary number, and time of maximum for each date. In 

 Axt. Xacli., No. 3516, E. Abelmann, of St. Petersburg, 

 gives the results of his investigation of the orbit of the 

 associated comet (Tempel 18G6 I.) and meteoric swarm, 

 lie corroborates the previous researches of Adams and 

 Newton, and concludes that the orbits of the meteors and 

 parent comet have nearly coincided with each other from 

 a very remote time. He finds that the longitude of the 

 node is increased 31-5' during one revolution, or about 1-5^ 

 in a century. " As the stream has been observed for about 

 one thousand years, its line of apses has revolved in that 

 time about fifteen degrees, but a glance at the form of the 

 orbit shows that this motion of the apse would alter the 

 solar distance of the stream at the descending node very 

 little from the earth's distance from the sun, so that for 

 many ages yet the continued visibility of the star shower 

 will not be thereby affected. In front of the comet there 

 seems to be no train of dense matter, as at its passage 

 through the node in 1865, the earth was at a com- 

 paratively small distance from the comet, and meteors 

 were only remarked in small abundance. At the earth's 

 passage through the node in 1867, again, only a meagre 

 meteoric display was visible." Prof. Abelmanrrtseems to 

 have overlooked the splendid showers of Leonids seen in 

 America both in 1867 and 1868, and has apparently also 

 underrated the strength of the system in that part of the 

 orbit which precedes the cometary nucleus. The observation 

 in 1898 ought to produce important evidence on the latter 

 point. 



The Meteoric Shower of Biela's Comet. — This event, so 

 brilliantly presented in 1872 and 1885, and seen in fairly 

 conspicuous character in 1892, may return again in 1898, 

 on November 23rd or 24th. But the period of six years, 

 elapsed since 1892, is less than that of the parent comet, 

 though the year 1898 corresponds with the thirteen-year 

 interval between 1872 and 1886. The average period of 

 Biela's comet, derived from observations between 1772 and 

 1852, was 6'71 years, but the time was apparently shorten- 

 ing, for between 1772 and 1826 it was 6-76 years, while 

 between 1826 and 1852 it was only ()62 years. It is most 

 unfortunate that the comet has not been re-observed since 

 1852, and that we can only judge its exact whereabouts by 

 the most brilliant return of the meteoric system with which 

 it seems to be intimately connected. On November 23rd 

 next the earth will probably become involved in that 

 section of the stream just preceding the comet, and the 

 shower may quite possibly be a very plentiful one, for in 

 1838 the earth crossed the orbit far in the van of the comet, 

 and yet a rich display occurred. But the precise character 

 of the approaching rencontre cannot be defined. The 

 period of thirteen years between the shower of 1872 and 

 1885 may not apply with equal force to future returns. In 

 1872 the earth was immersed in the material lying in the 

 wake of the comet, while in 1885 it was involved with that 

 in front of it, so that in 1)S98 we shall pass yet further in 

 front, and possibly too far in advance of the cometary 

 nucleus to witness a really imposing flight of meteors. If, 

 however, the period of revolution has decreased since 1852, 

 and the meteoric stream is in process of distending itself 

 along the orbit, then a fine display may occur this year. 

 In any case, it should be attentively looked for on the 

 nights of November 23rd and 24th. The moon will be in 

 a gibbous phase, and visible during the <,'reater part of the 

 night. There will, however, be several hours of dark sky 



