ASTRONOMICAL PANICS. 195 



not be very wonderful that it should reappear now after thirty-seven 

 years, instead of one hundred and seventy-five years. The velocity of 

 a body moving in the solar system depends simply on its distance from 

 the sun, and on the major axis of its orbit. If the velocity is reduced 

 by a resisting medium, there will be a reduction of the major axis, and 

 there is nothing whatever unreasonable in the supposition that, how- 

 ever weak the corona may be, its resistance would have a very great 

 effect upon the motion of a comet which rushes through it, so that I 

 should not be at all surprised if it should turn out that this comet of 

 1880 is the same as the comet of 1843 and that of 1668, and that its 

 revolution has been so much affected that possibly it may return in, 

 say, seventeen years." 



These remarks of Mr. Marth were some time since quoted by Mr. 

 Proctor, and made the basis of an article which in unscientific circles 

 produced to some extent a most absurd sensation. Mr. Proctor's re- 

 marks on the subject have been misinterpreted as indicating the prob- 

 able destruction of life upon the earth about the close of the present 

 century. His language, however, though somewhat unguarded, ex- 

 pressed no such opinion. 



The three comets named above approached nearer the sun than 

 any other known, except, perhaps, that of 1680. In fact, when nearest 

 the sun they actually grazed the solar atmosphere, or passed through 

 its outermost portions. Now, it is well known that the motion of a 

 planet or comet through a resisting medium continually lessens its 

 distance, and hence accelerates its velocity. Messrs. Marth and Proc- 

 tor assume that the passage of the comet of 1668 through the outer 

 portions of the sun's atmosphere reduced its previously long but un- 

 known period to one hundred and seventy-five years, so that its next 

 appearance was in 1843. The perihelion distance at that date was 

 still less ; the comet met with greater resistance, and the period was 

 shortened to thirty-seven years. The time of revolution would thus 

 be lessened at each successive return, and ultimately the comet would 

 plunge into the sun. Striking the solar surface with a velocity of 

 three hundred and fifty miles a second, the amount of heat produced 

 by the concussion and radiated to the earth might raise the tempera- 

 ture to such a degree as to destroy life upon our planet. Such are the 

 conjectures suggested in Mr. Proctor's paper. Let us briefly consider 

 them. 



In the first place, the fact on which the theory of the supposed 

 catastrophe is based viz., the identity of the three comets is extreme- 

 ly doubtful. It is much more probable, in view of all the circum- 

 stances, that they are different bodies moving in similar orbits. 



Again, the period of seventeen years, fixing the comet's next re- 

 turn, according to Mr. Marth, about 1897, was the merest conjecture, 

 not founded on any mathematical calculation whatever. It is true 

 that the passage o a comet through the sun's atmosphere would short- 



