404 ANNUAL OF SCIENTIFIC DISCOVERY. 



seen as a solar phenomenon in a total eclipse of the sun, in the corona or 

 halo that encircles the sun concealed behind the dark body of the moon, 

 the aigrettes that stream out in various directions, and perhaps also the rose- 

 colored flames that here and there project beyond the dim circular disk of 

 the moon. 1 



Professor Peirce's Vieivs on Comets. The following; statement of views on 

 comets is reported to have been made by Professor Peirce, of Cambridge, to 

 the French Academy; the results being predicated from observations on 

 Donati's comet of 18-38: 



The nucleus is of a metallic density, van-ing from three to twenty, if the 

 density of water be taken as unity, and it is surrounded by an immense 

 atmosphere. Under the influence of the sun's heat, matter is given off from 

 the nucleus, forming an envelope, which rises with uniform velocity. As it 

 rises it becomes electric, like a cloud, and is repelled by the electricity of the 

 sun ; and when the solar influence becomes strong enough to overcome the 

 natural cohesive force of the envelope, the latter separates from the comet 

 and becomes the tail. The most electrified particles of the tail are those of 

 the anterior surface; the other particles have much less electricity, the 

 degree depending on their distance from this anterior surface. Prof. Peirce 

 suggests the same explanation (viz., the electrical action) for some of the 

 hitherto unexplained and apparently causeless movements of the heavenly 

 bodies; among others, the erratic movements of Mercury, recently proved 

 by LeVerrier. He states that the nucleus of Donati's comet was less than 

 one hundred and fifty miles in diameter, while the atmosphere had a diame- 

 ter of forty thousand miles; that the envelope, in that case, rose from the 

 nucleus at the rate of about thirty miles an hour: and that the strength 

 of the electric influence of the sun was such as to destroy gravitation, and 

 give a force repelling the tail from the sun equal to two and a half, if the 

 attraction of gravitation be taken as unit}'. In that case, however, some of 

 the particles of the tail were so feebly electrified that their repulsive force 

 was overcome by the attraction of gravitation. 



Mr. Kemplay's TJteory of Comets. The following theory, brought for- 

 ward in England by Mr. Kemplay, has at least the merit of novelty. He 

 supposes that a comet is " a body of gaseous matter, homogeneous and indis- 

 tinguishable in its parts, and nearly, but not perfectly, transparent." The 

 form which a body of this nature, moving, as comets do, round the sun in a 

 very elliptical orbit, would assume under the combined influences of the 

 internal attraction of its particles and the external attraction of the sun, 

 would be that of a prolate spheroid, or oval, with its major axis in the direc- 



1 It would seem that even the visible nucleus of a comet is not in a truly stati- 

 cal condition. It contracts and enlarges with the varying distance from the 

 sun. This may be a mere appearance, arising from the varying luminosity of the 

 photosphere. It is also possible that the inner nucleus, with its atmosphere, may be 

 surrounded by an ethereal atmosphere, which contracts and expands by reason of 

 variations in an impulsive action of the sun, and in the density of the ether of 

 space in the vicinity of the sun. These remarks may also apply to the entire en- 

 velope of Encke's comet, and the complete spherical envelopes sometimes noticed. 

 Spherical envelopes, entirely surrounding the nucleus, would also be formed, if the 

 cometic matter should be projected from all parts of the nucleus with the same 

 velocity, but with a force insufficient to overcome the gravitating tendency. An 

 apparent spherical continuation of an envelope behind the nucleus might, perhaps, 

 result from the intersections of the orbits of the cometary particles urged past it 

 iuto space by the repulsive force of the sun. 



