THE GREAT COMET OF 1882. 



297 



On September 17th the comet passed its perihelion at a distance of 

 about 750,000 miles from the sun's center, and witbin 300,000 of its 

 surface, rushing through the coronal regions with a velocity exceeding 

 300 miles per second: it swept over 180 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 1608, 1G80, 

 1843, and 1880. (As to the comet of 1008 there is some doubt, be- 

 cause it was only observed for about three weeks, and its motion dur- 

 ing that time was such that it answers almost equally well to either of 

 two quite different orbits.) There are half a dozen others with peri- 

 helion distances between one and a half and five million miles, viz., 

 comets of 1707, 1810, 1820, 1847, 1805, and 1870 ; and Wells's comet, 

 which disappeared only a few weeks ago, is just outside that limit, 

 with a perihelion distance of 5,075,000 miles. Now, as to the comets 

 of the first class, we find that, excepting that of 1080, their orbits 

 are extremely similar ; their plane and direction 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 

 liave all come toward the sun from the same region of the heavens, in 

 the immediate neighborhood of the great star Sirius. In the little 

 table below are given what are called the elements of their orbits: 

 9, is the longitude of the node, i the inclination of the orbit to the 

 ecliptic, n the longitude of the perihelion, and q the perihelion dis- 

 tance, 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 de- 

 notes that the motion is retrograde. The orbits of the first tw T o are 



from the catalogue in Chambers's " Descriptive Astronomy " ; that of 

 1880 is the orbit computed by Meyer, of Geneva, from the whole as- 

 semblage of observations, and that of 1882 is the last orbit computed 

 by Mr. Chandler, of Cambridge, and may be found to need some cor- 

 rection when later observations come to hand. Fig. 4 shows 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. 



Now, the similarity between these orbits may be explained in two 

 different ways. It might be accounted for by supposing that we have 

 to do with different visits to the sun of a single comet, or that Ave 

 have here a group or family of comets, very likely of common origin, 



