COMETS' TAILS. 269 



comet. 5thly. Tliat the force thus acting on the materials of the tail cannot 

 possibly be identical with the ordinary gravitation of matter, being centrifugal 

 or repulsive, as respects the sun, and of an energy very far exceeding the 

 gravitating force towards that luminary. This will be evident if we consider 

 the enormous velocity with which the matter of the tail is carried backwards, 

 in opposition both to the motion which it had as part of the nucleus, and to 

 that wliich it acquired in the act of emission. 



Again, describing the long straight tail of the great comet of 1843, 

 from which a lateral tail, nearly twice the length of the regular one, 

 was shot forth in a single day, Herschel says : 



The projection of this ray, which was not seen either before or after the 

 day in question, to so enormous a length (nearly 100°) in a single day conveys 

 an impression of the intensity of the forces acting to produce such a velocity 

 of material transfer through space, such as no other natural phenomenon is 

 capable of exciting. It is clear that if we have to deal here vnth matter, such 

 as we conceive it, viz., possessing inertia, at all, it must be under the dominion 

 of forces incomparably more energetic than gravitation, and quite of a different 

 nature. 



And finally (p. 406) : 



There is beyond question some profound secret and mystery of nature con- 

 cerned in the phenomenon of their tails. In no respect is the question as to 

 the materiality of the tail more forcibly pressed on us for consideration than 

 in that of the enormous sweep which it makes round the sim in perihelio, in 

 the manner of a straight and rigid rod, in defiance of the law of gravitation, 

 nay, even of the received laws of motion, extending (as we have seen in the 

 comets of 1680 and 1843) from near the sun's surface to the earth's orbit, yet 

 whirled round unbroken, in the latter case through an angle of 180° in little 

 more than two hours. It seems utterly incredible that in such a ease it is one 

 and the same material object which is thus brandished. If there could be con- 

 ceived such a thing as a negative shadoic, a momentary impression made upon 

 the luminiferous ether behind the comet, this would represent in some degree 

 the conception such a phenomenon irresistibly calls up. But this is not all. 

 Even such an extraordinary excitement of the ether, conceive it as we will, will 

 afford no accoimt of the projection of lateral streamers; of the effusion of light 

 from the nucleus of a comet towards the sun; and of its subsequent rejection; 

 of the irregular and capricious mode in which that effusion has been seen to 

 take place. 



These passages give a vivid picture of the utter puzzledom of 

 astronomers over difficulties which arise from precisely those phe- 

 nomena which fit most naturally into the theory of Arrhenius. 



The Prominences and the Corona. 

 At the moment when the sun's disc is obscured in a total eclipse 

 enormous red flames, sometimes curving over towards the sun and 

 sometimes floating like clouds at heights up to 40,000 miles above his 

 surface, are seen projecting over the region of sunspots, where the sun's 

 eruptive activity is greatest; and silvery streamers with a radial struc- 

 ture form a lens-shaped envelope about the same region, often extending 



