122 On the Formation of the Tails of Comets. 



is, that whenever a comet, which has its perihelion near the sun, 

 (as the comets of 1843 and 1680,) sweeps around the sun, the 

 great centrifugal force generated by the amazing velocity of rota- 

 tion would entirely dissipate the greater part of the tail. It may 

 be well to remark, in this connection, that the supposed rotation 

 of a comet would, in general, dissipate the tail more or less rap- 

 idly, unless the particles should be held together by a strong 

 molecular attraction. For, I find, that taking the mass of the 

 head as great as the T ol^o P art °f the mass of the earth, and 

 supposing the rate of rotation to be only 2° per day, the centri- 

 fugal force will be equal to the gravitation towards the head at 

 the distance of only 39,000 miles. In the case of the comet of 

 last year, this equality subsisted, at the time of the perihelion 

 passage, at the very small distance of 434 miles from the centre 

 of the nucleus. These examples will serve to show, that on the 

 theory now under consideration the centrifugal force must be 

 supposed to play an important part in the elongation of the tail. 

 Another of the consequences of this theory at variance with ob- 

 servation is, that the velocity of rotation communicated in the 

 approach to the sun, being still retained after the passage of the 

 perihelion, and being continually augmented by the action of the 

 force which is the operative cause of the rotation ; when the tail 

 comes up into opposition, it ought soon to get in advance of this 

 position, and more and more from day to day until the velocity of 

 rotation becomes reduced to an equality with that of revolution, by 

 the action of the force on the other side of the centre of gravity. 

 Other considerations might be urged corroborative of the evidence 

 already obtained of the fallacy of the common notion that all 

 the parts of a comet are united into one revolving and rotating 

 mass ; but it is time that I proceeded to give a more detailed ex- 

 position of the other conception to which I referred in the begin- 

 ning of this article, and to furnish such direct arguments in sup- 

 port of it as my limits will admit. 



The theory that cometic matter continually flowing away from 

 the head of a comet constitutes what is called the tail, first occur- 

 red to me while preparing an article on the subject of the recent 

 comet, subsequently published in the Philadelphia Inquirer of 

 April 25th : and it is there given, in its incipient state, as a mere 

 suggestion — the intimation being at the same time given that, 

 although new to the writer, it had, in all probability, previously 



