70 



KNOWLEDGE 



[March 1, 1898. 



with their stem and two lash-like branches {see Fig. q), do 

 not awake in him at least a suspicion that the crustacean 

 family is not only not confined to a few articles of domestic 

 consumption, but may have ramifications even beyond the 

 bounds of the Malacostraca. 



NOTES ON COMETS AND METEORS. 



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



Comets. — Pons-Winnecke's comet at the beginning of 

 March will enter the head of Capricornus and pass between 

 the bright stars a and /3 of that constellation ; but as these 

 objects will be only forty degrees west of the sun, and rise 

 about two hours before him, there will be but a slender 

 prospect of observing the comet. The distance of this 

 object from the earth is now increasing, and it is not likely 

 to be seen again in ordinary telescopes until the early part 

 of 1904. 



Comet II. 1892 (Denning).— In Ast. Nac/i. 3472, Dr. 

 Steiner, of O'Gyalla, Hungary, gives a definite orbit which 

 he has derived for this object from a discussion of one 

 hundred and eighty-six observations. Though a very 

 small, faint comet, it was visible for a long period, and its 

 positions were secured during the ten months from 1892, 

 March 19th, to 1893, January 12th. Dr. Steiner con- 

 cludes that the orbit is hyberbolic, for, with the excentricity 

 at 1-000345, the sum of the squares of the residuals is 

 103-2" for an hyperbola, and 279-5" for the parabola. 

 The observations near the middle of the series, in the 

 summer of 1892, exhibit rather large residuals, and Dr. 

 Scheiner regards this as unsatisfactory. But the comet 

 was difficult to observe at that time owing to the twilight, 

 and to its faintness, due to great distance from the earth ; 

 for at the middle of June the comet was separated from us 

 by an interval of two hundred and seventy millions of 

 miles. The path of the comet was nearly vertical to the 

 ecliptic, the inclination being eighty-nine and three-quarter 

 degrees. Dr. Scheiner's definitive elements are : — 



T 1892, May 11-201935 M.T. Berlin. 



ir 22° 45' 42-40" 



n 253° 25' 50-92" 



I 89° iV 54-10" 



log. ,]. ... 0-2946197 



e 1-000345 



Meteors. — Though the shower of Leonids in 1897 was 

 not very brilliant, and completely obscured by clouds at 

 the majority of stations on the mornings of November 

 15th and 16th, it returned with fair activity on those dates. 

 There is little doubt, however, that the earth did not 

 encounter the really dense portion of the stream, but it is 

 difficult to specify what strength is fairly representative of 

 the main swarm, and a certain standard (or rate of appari- 

 tion) will have to be adopted to express it. The richest 

 part of the current is probably not a sudden development, 

 but due to gradually increasing abundance along a con- 

 siderable stretch of the orbit. It is important to ascertain 

 the time when the earth encounters that section of the 

 stream in which the meteors begin to be thickly congre- 

 gated. In 1833 there were one thousand meteors per 

 minute, while at about the period of maximum frequency 

 on November 13th, 18G6, there were one hundred per 

 minute for one observer. What, therefore, will be the 

 rate of appearance assumed for the fore region of the 

 main swarm ? Perhaps ten meteors per minute might 

 satisfactorily represent it, for this would give six hundred 

 per hour, it being understood that the figures are for one 

 observer watching a clear, moonless sky with the radiant 

 at a fair altitude. It is certain from the conditions of the 



case that the relative intensity of the stream at different 

 parts can only be ascertained after many cyclical returns 

 of the swarm, for the earth is only involved in it for a 

 short time once a year, and in the interim of successive 

 encounters a vast range of the current passes the node 

 without recognition. 



Now that the efi'ort is being made to photograph the 

 group of Leonid meteors in space, it might be as well to 

 endeavour to get an impression of the parent comet. On 

 March 10th the comet will be certainly less than two 

 liundred millions of miles distant, and possibly less than 

 one hundred and fifty millions, whereas the meteoric 

 swarm will be about five hundred and sixty-eight millions 

 distant on the same date. In view of the fact that the 

 comet is more highly condensed and probably far more 

 luminous than its accompanying meteoric stream, the pro- 

 spect of detecting it is much more favourable. Towards the 

 close of the present year, however, the comet will approach 

 much nearer to the earth than it is at present, and no 

 doubt some special efforts will then be made to redetect it. 



Fireball of 1898, January 21st. — In the twilight of 

 Friday evening, January '21st, at 5h. 32m., one of those 

 large fireballs which occasionally burst out and illuminate 

 sky and landscape with startling brilliancy, was observed 

 at a great many places in the South of England, and in 

 some parts of Ireland and Wales. A considerable number 

 of descriptions of the object were published in the news- 

 papers, and if, as usual, the writers failed to record the 

 exact position of the meteor's path and its duration of 

 flight, they one and all testified to the astonishing brilliancy 

 of the phenomenon. Not many stars were visible at the 

 moment of the meteor's descent, so it was diflScult to fix 

 its apparent course with the necessary precision. But 

 several of the observers were fortunate enough to obtain a 

 good \aew of it, and recorded the path as accurately as 

 circumstances permitted. From thirty-three accounts 

 which I have compared together, it appears certain that 

 the fireball traversed a very long path from east to west 

 over the south coast of Enijland. Observers in London 

 and that district say that the object first appeared at a 

 great altitude in south-east or south, and disappeared in 

 south west ; while spectators in the western counties 

 describe the motion as from east or east by south to south- 

 west, or south-west by south. The flaming nucleus was 

 not so large as the moon, but was, according to several 

 reports, about twelve or fifteen minutes of arc in diameter, 

 but its brightness exceeded that of the full moon. The 

 colour appears to have varied, and observers are by no 

 means agreed in their estimations, but the head seems to 

 have been yellowish and the train bright green and purple. 

 The meteor burst before vanishing ; and it travelled, not 

 with that very slow, sailing flight which is often charac- 

 teristic of the largest fireballs, but with moderate velocity, 

 and its entire visible course probably occupied seven seconds. 

 One person, however, says it lasted thirty seconds ; another 

 estimated the duration as nearly five minutes ! The best 

 estimates vary from three to seven seconds, but most of 

 the observers only caught the meteor after it had akeady 

 traversed a part of its course, and when it was descending 

 at a low altitude in the south-west. 



The fireball when first seen appears to have been 

 eighty-two miles above a point five miles south of Croydon 

 in Surrey. Moving to the south-west by west it passed 

 over Peterstield, Lymington, and St. Alban's Head, and 

 disappeared at a height of twenty-five miles over the 

 English Channel some thirty-five miles south of Eddystone 

 Lighthouse. Its length of path was two hundred and 

 thirty-five miles, and velocity about thirty-four miles per 

 second. The radiant point was in the north-east region 



