p>' 



REPORT— 1871. 



the group of meteors which extends over a portion of the orbit so great 

 as to occupy about one-tenth ,or one-fifteenth of the periodic time in 

 passing any particular point, and gave a choice of five different periods for 

 the revolution of this meteoric stream round the sun, any one of which would 

 satisfy his statistical result. He further concluded that the line of nodes 

 (that is to say, the line in which the plane of the meteoric belt cuts the plane 

 of the Earth's orbit) has a progressive sidereal motion of about 52"-4 per 

 annum. Here, then, was a splendid problem for the physical astronomer ; 

 and, happily, one well qualified for the task, took it up. Adams, by the 

 application of a beautiful method invented by Gauss, found that of the five 

 periods allowed by Newton just one permitted the motion of the line of nodes 

 to be explained by the disturbing influence of Jupiter, Saturn, and other 

 planets. The period chosen on these grounds is 33| years. The inves- 

 tigation showed further that the form of the orbit is a long ellipse, giving 

 for shortest distance from the Sun 145 million kilometres, and for longest 

 distance 2895 million kilometres. Adams also worked out the longitude 

 of the perihelion and the inclination of the orbit's plane to the plane of the 

 ecliptic. The orbit which he thus found agreed so closely with that of 

 Temple's Comet I. 1866 that he was able to identify the comet and the 

 meteoric belt *. The same conclusion had been pointed out a few weeks 

 earlier by Schiaparelli, from calculations by himself on data supplied by 

 direct observations on the meteors, and independently by Peters from calcu- 

 lations by Lcverrier on the same foundation. It is therefore thoroughly 

 established that Temple's Comet 1. 1806 consists of an eUiijtic train of minute 

 planets, of which a few thousands or millions fall to the earth annually about 

 the 14th of November, when we cross their track. We have probably not 

 yet passed through the very nucleus or densest part ; but thirteen times, in 

 Octobers and Novembers, from October 13, a.d. 902, to November 14, 1866 

 inclusive (this last time having been correctly predicted by Prof Newton), 

 Ave have passed through a part of the belt greatly denser than the average. 

 The densest part of the train, when near enough to us, is visible as the head 

 of the comet. This astounding result, taken along mth Huggins's spectro- 

 scopic observations on the light of the heads and tails of comets, confirms 

 most strikingly Tait's theory of comets, to which I have already referred ; 

 according to which the comet, a group of meteoric stones, is self-luminous 

 in its nucleus, on account of collisions among its constituents, while its " tail " 

 is merely a portion of the less dense part of the train illuminated by sunlight, 

 and visible or invisible to us according to circumstances, not only of density, 

 degree of illumination, and nearness, but also of tactic arrangement, as of a 

 flock of birds or the edge of a cloud of tobacco-smoke ! "Wliat prodigious diffi- 

 culties are to be explained, you may judge from two or three sentences which 



* Signer Schiaparelli, Director of the Observatory of Milan, who, in a letter dated Slst 

 December LS66, pointed out that the elements of the orbit of the Angust Meteors, calcu- 

 lated from the observed position of their radiant point on tlic supposition of the orbit 

 being a very elongated ellipse, agreed very closely veith those of the orbit of Comet II. 1862, 

 calculated by Dr. Oppolzer. In the same letter Schiaparelli gives elements of the orbit 

 of the November meteors, but these veere not suiTiciently accurate to enable him to identify 

 the orbit vrith that of any knovfn comet. On the 21st January, 1867, M. Leverrier gave 

 more accurate elements of the orbit of the November Meteors, and in the ' Astronomiscbo 

 Nachricliten ' of January 9, Mr. C. F. W. Peters, of Altona, pointed out that these elements 

 closely agreed with those of Temple's Comet (I 18G6), calculated by Dr. Oppolzer; and 

 on February 2, Schiaparelli having recalculated the elements of the orbit of the meteors, 

 himself noticed the same agreement. Adams arrived quite independently at the conclusion 

 that the orbit of 33^ years period is the one which must be chosen out of the five indi- 

 cated by Prof. Nevrton. His calculations were sufficiently advanced before the letters 



