THE GREAT COMET OF 1882. 299 



haps not sufficient to settle the orbit definitively, seem to be absolutely- 

 inconsistent with a period of anything like three years (corresponding 

 to an eccentricity of 0*9963). The period can not well be 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 Q, and q, the two 

 orbits differ more than can well be consistent with the theory of iden- 

 tity. It seems to be an almost necessary consequence that these two 

 comets can not be identical with each other, though they may, per- 

 haps, both be fragments of the comets of 1668 or 1843, or of some 

 comet more ancient than either. 



It is an interesting fact that Mr. Chandler finds that his orbit, com- 

 puted entirely from post-perihelion observations, satisfies almost ex- 

 actly 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 observations of Dr. Gould, when they come to hand, agree as well, 

 it will be proof positive that no sensible resistance or disturbance of 

 any kind was suffered by the comet in passing within 300,000 miles 

 of the sun's surface at the rate of 300 miles a second. 



Of course, if the view we have taken is correct, there is no possi- 

 bility that our comet can return in six months and fall into the sun. 

 Not that there is any absurdity in the idea by itself considered. If 

 the comet of 1880, when receding from the sun, had moved in an orbit 

 corresponding to a three years' period, and if the present comet were 

 found to have a period of three years or less as it is now receding from 

 the sun, it would be almost impossible to refuse to admit their iden- 

 tity, and probable speedy absorption in the sun. 



We close with a single word as to the probable consequences of a 

 comet's fall upon the sun. Unquestionably, the energy of the comet's 

 motion would be transformed into heat, and if the comet had any con- 

 siderable mass, say y^- the mass of the earth, the heat produced would 

 be enough to supply the sun's heat-expenditure for months. Prob- 

 ably, however, no comet has a mass anything like so great as that ; 

 more likely the present comet even, huge as it is, has a mass less than 

 j 0*0 of the earth's, so that its collision with the sun would produce 

 as much heat only as the sun would expend in eight hours. 



Now, if the sun were a cool, solid, or even liquid mass, the sudden 

 accession of merely this quantity of heat would undoubtedly produce 

 an enormous rise of temperature and a great increase of radiation. 

 But, constituted as the sun is mainly a mass of gas and vapor the 

 effect would be entirely different, the energy being principally ex- 

 pended in producing expansion and evaporation, with comparatively 

 little increase of temperature or radiation. If one stirs up the fire 

 under an open kettle, the water gets no hotter it only boils faster. 

 Probably the effect of the fall of a body, even as large as the earth, 

 upon the sun, would be hardly anything more than to restore the sun 

 to the condition it was in a century ago. The energy lost in the course 



