March 30, 1333.] 



♦ KNOWLEDGE ♦ 



195 



THE GREAT COMET OF 1882.— IV. 

 Uy Professor C. A. Young. 



(Continued from page liU.) 



ON Sept. 17 the comet passed its perihelion at a 

 distance of about 750,000 miles from the sun's 

 centre, and within 300,000 of its surface, rushing through 

 the coronal regions with a velocity exceeding 300 miles per 

 a'-coiid : it sw4'pt over lt*0° of its orbit in three hours and 

 a-half. Thus far we find in our lists of cometary orbits 

 only four with so small a perihelion distance, viz., the 

 comets of 1GG8, 1680, 1813, and 1880. (As to the comet 

 of 16G8 there is some doubt, because it was only ol^servcd 

 for about three weeks, and its motion during that time 

 was such that it answers almost equally well to either 

 of two quite different orbits.) There are half-a-dozen 

 others with perihelion distances Vietwccn one and a-half 

 and five million miles, viz., comets of 1767, ISIO, 182G, 

 1847,1865, and 1870; and Wells's comet, which dis- 

 appeared only a few weeks ago, is just outside that limit, 

 with a perihelion distance of .">,67.'i, 000 miles. 

 Now, as to the comets of the first class, we 

 find that, excepting that of 1680, their orbits 

 are extremely similar ; their plane and direc- 

 tion of motion are almost exactly the same ; 

 the perihelion distances are nearly the same 

 for all ; and the axes of the orbits all point 

 to the same part of space ; they have all come 

 toward the sun from the same region of the 

 heavens, in the immediate neighbourhood of 

 the great star Sirius. In the little table 

 below are given what are called the elements 

 ■of their orbits : Q is the longitude of the 

 node, i the inclination of the orbit to the 

 ecliptic, - the longitude of the perihelion, and 

 q the perihelion distance, expressed .as a 

 decimal fraction of the earth's distance from 

 the sun ; e is the eccentricity of the orbit ; 

 and the — in the last line denotes that the 

 motion is retrograde. The orbits of the first 

 two are from the catalogue in Chambers's 

 " Descriptive Astronomy ' ; that of 1880 is 

 the orbit computed by Jleyer, of Genevr, 

 from the whole assemblage of observation', 

 and that of 1882 is the last orbit comput(d 

 by Mr. Chandler, of Cambridge, and may 1 ■■ 

 found to need some correction when late 

 observations come to hand. Fig. 4 shoves 

 in a rough way how these orbits 'lie in relation to the 

 orbit of the earth, and how very long and narrow the 

 comet's orbit is as compared with the circle described by 

 the earth. 



their identity. The ditlerences are no greater than probable 

 perturbations might account for. Then, again, the comets of 

 1843 and 1880 may easily be identical. Indeed, the orbit 

 given for the latter comet corresponds to a period of almost 

 thirty-seven years, and Meyer has shown that the observa- 

 tions cannot be reconciled with a period less than thirty 

 or greater than fifty years. Now, thirty-seven years would 

 take us back just to 1843, so that it is very likely that 

 these two comets are really one and the same. So far the 

 "identifiers" have matters their own way. But now, as 

 to the comet of 1882. Can it be identical with the comet 

 of 1880? We think not. The orbit of the latter was 

 computed exclusively from observations taken after its 

 perihelion passage, so that no action of the s^m depending 

 upon its close approach at perihelion can account for its 

 return in less than three years, and the inclination of its 

 orbit is such that ever since it went out of sight it has 

 been out of harm's way as to perturbations by the planets. 

 Then, again, the orbit of the comet of 1882 does not agree 

 with the idea of identity. Whatever other effects may 

 have been produced by the resistance of the solar atmo- 



Sl 



1668. 

 .... 357' 17' 

 35° 58' 



«■ 277° 2" 



J 00047 



e 10 



Direction ... — 



1843. 

 301° 12" 



35° 41' 

 278' 39' 

 00055 

 0-99989 . 



1880. 

 35G° 17' 



36° 53' 

 278° 23' 

 00059 

 0-99947 



18B2. 

 315° 50' 



38' 05' 

 270° 28' 

 0-0076 

 0-99997 



Now, the similarity between these orbits may be 

 explained in two ditFerent ways. It might be accounted 

 for by supposing that -ne have to do -with different visits 

 to the sun of a single comet, or that we have here a 

 group or family of comets, very likely of common origin, 

 but separate, and following each other. Hoek, of 

 Utrecht, showed some years ago that such comet-families 

 exist. When we compare the orbits of the comets of 

 1843 and 1668 there is nothing that forbids the idea of 



sphere at perihelion, this resistance must have tend 

 to shorten its period, if it changed it at all. No 

 the observations thus far tak(>n, though perhaps not 

 sufficient to settle the orbit definitely, seem to be abso- 

 lutely inconsistent with a period of anything like three 

 years (corresponding to an eccentricity of 0'9963). The 

 period can not be well less than ten or twelve years, 

 according to the last results, and may be several thousand. 

 It is to be noted, further, that, as regards ft and q, the two 

 orbits differ more than can well be consistent with the 

 theory of identity. It seems to be an almost necessary 

 consequence that these two comets cannot be identical 

 with each other, though they may, perhaps, both be frag- 

 ments of 1668 or 1843, or of some comet more ancient than 

 either. 



It is an interesting fact that Mr. Chandler finds that his 

 orbit, computed entirely from post-perihelion observations, 

 satisfies almost exactly the observation of Mr. Finlay, 

 taken on September 8th, as well as the observation of the 

 comet's disappearance at the sun's edge. If the obserra- 



