in an unresisting medium. This difficulty will, however, be removed, if it be 

 remembered that a resisting medium, by diminishing the velocity of the body 

 in its orbit, diminishes the influence of the centrifugal force to resist solar at- 

 traction. The body, therefore, follows a path consiantly nearer to the sun ; in 

 other words, the orbit is in a progressive state of diminution. Now, the less 

 the orbit is, the less time necessary to describe it ; and consequently the shorter 

 the period of the successive returns of the body to the same position. 



If the successive returns of the periodic comets should establish satisfacto- 

 rily the existence of the luminous ether, it will follow that after the lapse of a 

 certain time every comet will ultimately fall into the sun. In every succeed- 

 ing revolution of the same comet, its path would fall a little within its former 

 course, and it woujd describe a spiral line round the sun, continually approach- 

 ing that body, until at length it would arrive close to its surface ; before this 

 could happen, it would doubtless be wholly converted into a light gas by his 

 heat, which would probably mingle with the solar atmosphere. 



In the efforts by which the human mind labors after truth, it is curious to 

 observe how often that desired object is stumbled upon by accident, or arrived 

 at by reasoning which is false. One of Newton's conjectures respecting com- 

 ets was, that they are " the aliment by which suns are sustained ;" and he 

 therefore concluded that these bodies were in a state of progressive decline 

 upon the suns, round which they respectively swept ; and that into these suns 

 they from time to time fell. This opinion appears to have been cherished by 

 Newton to the latest hours of his life : he not only consigned it to his immor- 

 tal writings, but, at the age of eighty-three, a conversation took place between 

 him and his nephew on this subject, which has come down to us. " I cannot 

 say," said Newton, " when the comet of 1680 will fall into the sun : possibly 

 after five or six revolutions ; but whenever that time shall arrive, the heat of 

 the sun will be raised by it to such a point, that our globe will be burnt, and 

 all the animals upon it will perish. The new stars observed by Hipparchus, 

 Tycho, and Kepler, must have proceeded from such a cause, for it is impossi- 

 ble otherwise to explain their sudden splendor." His nephew then asked him, 

 " why, when he stated in his writings that comets would fall into the sun, did 

 he not also slate those vast fires they must produce, as he supposed they had 

 done in the stars ?" " Because," replied the old man, " the conflagrations of 

 the sun concern us a little more directly. I have said, however," added he, 

 smiling, " enough to enable the world to collect my opinion." 



It may be asked, if the existence of a resisting medium be admitted, whether 

 the same ultimate fate must not await the planets ? To this inquiry it may be 

 answered that, within the limits of past astronomical record, the ethereal me- 

 dium, if it exist, has had no sensible effect on the motion of any planet. That 

 it might have a perceptible effect upon comets, and yet not upon planets, will 

 not be surprising, if the extreme lightness of the comets compared with their 

 bulk be considered. The effect in the two cases may be compared to that of 

 the atmosphere upon a piece of swan's down and upon a leaden bullet moving 

 through it. It is certain that whatever may be the nature of this resisting me- 

 dium, it will not, for many hundred years to come, produce the slightest per- 

 ceptible effect upon the motions of the planets. 



BIELA'S COMET. 



On February 28, 1826, M. Biela, an Austrian officer, observed in Bohemia 

 a comet, which was seen at Marseilles about the same time by M. Gambart. 

 The path which it pursued was observed to be similar to that of comets which 

 had appeared in 1772 and 1806. Finally, it was found that this body moved 



