558 



NATURE 



{Oct. 4, 1 888 



in the sky. The point from which they proceed in the case of 

 the swarm we are now considering lies in the constellation Leo, 

 situated in longitude 142 and latitude 8° 30' N., according to 

 Prof. Newton. 



The radiants are generally of short duration, but Mr. Denning 

 has shown that there are cases in which falling stars emanate 

 from the same part of the sky for long periods of time. 



One of these long-duration radiants between Auriga and 

 Taurus is shown in the accompanying illustration (Fig. 8). 



The next point, first brought to light by Olmsted, was that 

 during a display the radiant point moves with the stars across 

 the heavens. This is another strong argument in favour of the 

 cosmical theory. 



Meteors which are singly and occasionally observed, as we 

 have seen, are called sporadic meteors, but in addition to these, 

 which we may reckon to see every night, there are at certain 

 times of the year very well known falls ; so well known that we 

 can say at once that on the 10th or nth of next August more falling 

 stars will be seen than are ordinarily visible. These are termed 

 systematic meteors, and those to which we have just referred 

 as appearing in November are of this class. 



From 1833 to 1863 evidence was rapidly accumulated indicat- 

 ing that a very large proportion of the shooting-stars observed 

 were not sporadic, but really systematic — that is to say, that at 

 certain periods of the year meteors might be expected to diverge 

 from their appearance in a particular part of the sky, and in 

 greater numbers from that part than from elsewhere. 



Fig. 9. — Position of the long-duration radiant among the stars. 



During these years a considerable number of radiant points 

 had been made out, and therefore the existence of a considerable 

 number of streams or swarms had been suggested if not estab- 

 lished. In 1863, -Prof. H. A. Newton used these facts to 

 strengthen the cosmical hypothesis. 



The observations of Humboldt, modern observations, so to 

 speak, were repeated, as we have seen, in 1833, on the same day 

 (or one day later) of the same month on which Humboldt had 

 made his observation in 1799, and again one day later in 1866 

 there was a recurrence of the same thing. Now these dates are 

 separated by an equal interval of thirty-three years. The idea 

 of periodicity was therefore suggested both for this and other 

 displays, and gave rise to so great an interest in this question 

 that an inquiry was set afoot as to whether falls had been seen 

 before at previous intervals of thirty-three years, or whether it 

 was a new thing seen first by Humboldt in 1799, or possibly by 

 the Cumanese in 1766. 



Prof. Newton took up the inquiry, and was soon able to show 

 that the various chronicles of star-showers from the very earliest 

 times, when properly discussed, indicated that the streams 

 suggested by the observations since 1833 had really at variously- 

 recurrent intervals since the beginning of astronomical observa- 

 tion given indications of their existence. 1 He especially indicated 

 such cases of constant recurrences of showers in April, August, 

 November, and December. 



1 Silliwaris Journal, vol. xxxvi. p. 1^6, 1863. 



The discussion of the dates of these showers in the early 

 records showed a constant slow change of date in one direction 

 or the other. This obviously demonstrated that the showers 

 were independent of the tropical year —that is to say, of the 

 earth's motion round the sun ; and it is difficult to understand 

 how a more definite proof of their cosmical origin could be 

 afforded. 



We may conveniently confine our remarks on this point to 

 the inquiries relating to the "Leonid" swarm of meteorites 

 which gives rise to the November display. 



Newton and others found that we possess records, dating 

 from A.D. 902, showing that about every thirty- three years since 

 that time the heavens have been hung with gold. The Arab 

 historian, Abu-1'Abbas ad-Dimashki, chronicled the November 

 star-shower of the year 1202 of -our era in the following words, 

 the while Chinese astronomers carefully watched the constella- 

 tions in which the meteors appeared and vanished from the 

 sight : — 



" In the year 599, on the last day of Muharram, stars shot 

 hither and thither, and flew one against another like a swarm of 

 locusts ; this phenomenon lasted until daybreak ; people were 

 thrown into consternation, and made importunate supplications 

 to God the most High ; there was never the like seen except on 

 the coming out of the messenger of God — on whom be bene- 

 diction and peace." 



This table for the November display, from Prof. Newton, 

 shows what the result of searching the old records was : — 



Epochs of November Star-Showers. 



These ancient records enabled Prof. Newton to place the 

 planetary nature of the November ring beyond all doubt. 



It is evident that if this ring crosses our orbit in a certain defi- 

 nite point in space, our earth will always traverse it when it occu- 

 pies the same definite point of its orbit with regard to the 

 stars, provided the ring does not change its place. But 

 our ordinary year, called the tropical year, is affected by 

 the precession of the equinoxes, as it is measured from equinox 

 to equinox, so that we do not measure it by the stars, but by an 

 empirical point called the first point of the sign Aries, which 

 is actually at the present moment in the constellation Pisces. If 

 we refer the recorded star-showers to the sidereal year, or a fixed 

 equinox, we should find an almost absolute identity in the dates 

 of their appearance if there were no perturbation, but we shall 

 see subsequently that there is perturbation, and this is a final 

 demonstration of cosmical origin. 



If there is a swarm of meteorites falling in any particular 

 direction towards the plane of the ecliptic these meteorit 

 will take little account of the precession of the equinoxes 

 the tropical year ; the earth must take the meteorites as 

 finds them. The one great jump in the table was due to 

 alteration of the calendar, as there was a difference of twelve da 

 between the old and new reckoning. Prof. Newton, Pi- 

 Adams, and others have given a complete demonstration tl 

 from the year 902 a swarm of meteorites has been encounte 

 by the earth every thirty-three years or thereabouts, and nea 

 in the same part of her orbit round the sun. 



By a study of the position and lie of the earth in her orbit 

 can see from what part of space these meteors, these 

 numerous swarms, come. Suppose, for instance, that at 



1 H. A. Newton, Bui. Ac. R. Belg., xvii. No. 6. 



2 In many countries the change from old to new style was made in 

 interval commencing frcm 1582 in Spain, Portugal, and Ilaly. 



