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 Ω, 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 can not be identical with each other, though they may, perhaps, 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, 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 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 possibility 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 identity, 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 considerable mass, say 1100 the mass of the earth, the heat produced would be enough to supply the sun's heat-expenditure for months. Probably, 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 1100000 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 expended 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
