Trans N. V. Ac, Set. 'I'l Ocl. 30, 



///. Orbit and Motion. 



Prof. Boss, Director ot the Dudley Observatory at Albany, was the 

 first to point out the supposed identity of this comet with the comets 

 of 1843 and 1880, and prophesied its speedy return. 



Mr. Hind's elements also lead us to believe that the 1843 comet and 

 this one are the same. 



Mr. Proctor explains, in the last rwivnhtx ol Knowledge, how he was 

 misled, by the careless marking of a diagram, into a promise to show 

 that the great comet is to be seen where the comets of 1843 and 

 1880 could not have been seen. "I am unable to do so," he says, 

 " simply because there is every reason to believe that the comet, 

 which circled close around the sun on September 17, is no other 

 than our friend, the Menacing Comet, come back in less than two 

 years and eight months. The observations agree so well with the 

 theory that the comet is moving in the orbit of the comets of 1843 

 and 1880 (at least in the part of the orbit near the sun, for at aphe- 

 lion the orbit has been entirely changed), as to leave scarcely any 

 room for any doubt that the comet has come back again long be- 

 fore it was expected— how soon to return yet again, and how soon 

 to be finally absorbed by the sun, it were at present somewhat rash 

 to say." But after some further calculations, he says: "for my 

 own part — so far as observations hitherto made enable me to judge 

 — I expect the comet back in less than half a year.'' 



Some of you will recall the grand comet of 1843. AH remember the 

 beautiful appearance of the comet of 1880. The period calculated for 

 the 1843 comet was 175 years. If the supposition of Prof. BOSS is 

 correct, we have a change in the period of the comet from 175 to thirty- 

 seven years, and then to about three years. This immense change 

 must be ascribed to the resistance the comet meets with in passing so 

 close to the sun's surface, thus diminishing the linear velocity of the 

 comet, but increasing its angular velocity, and shortening its time of 

 revolution. The inevitable result of this must be a precipitation of 

 the comet into the sun. 



The comet of 1843 came within 500,000 miles of the sun's centre, or 

 70,000 miles of the sun's circumference. The comets of 1880 and of 

 1882 came nearly as close, if not closer. We know that the terrible 

 solar cyclones and volcanoes, if I may use the term, throw up masses of 

 hydrogen and other gases to a height more than sufhcient to surround 

 the head of the comet, when so near the sun. Moreover we know that 

 the mysterious coronal atmosphere extends many millions of miles out 

 from the sun. Thus the comet has to plough through this atmosphere, 

 and one would expect as a result a retardation in the motion of the 

 comet. 



