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 XXXI. Intelligence and Miscellaneous Articles. 



ON COMETS AND METEORS. BY DANIEL KIEKWOOD LL.D.j 

 PROFESSOR IN INDIANA UiMYERSTlTY*. 



n^HE comets which passed their perihelia in August 1862 and 

 -*- January 1866 will ever be memorable in the annals of science, 

 as having led to the discovery of the intimate relationship between 

 comets and meteors. These various bodies found revolving about 

 the sun in very eccentric orbits may all be regarded as similar in 

 their nature and origin, differing mainly in the accidents of magni- 

 tude and density. The recent researches, moreover, of Hoek, Le- 

 verrier, and Schiaparelli have led to the conclusion that such objects 

 exist in' great numbers in the interstellar spaces, that in consequence 

 of the sun's progressive motion they are sometimes drawn towards 

 the centre of our system, and that if undisturbed by any of the large 

 planets they again pass off in parabolas or hyperbolas. When, how- 

 ever, as must sometimes be the case, they approach near Jupiter, 

 Saturn, Uranus, or Neptune, their orbits may be transformed into 

 ellipses. Such, doubtless, has been the origin of the periodicity 

 of the August and November meteors, as well as of numerous 

 comets. 



In the present paper it is proposed to consider the probable con- 

 sequences of the sun's motion through regions of space in which 

 cosmical matter is widely diffused, to compare these theoretical 

 deductions with the observed phenomena of comets, aerolites, and 

 falling stars, and thus, if possible, explain a variety of facts in 

 regard to those bodies which have hitherto received no satisfactory 

 explanation. 



1. As comets now moving in elliptic orbits owe their periodicity 

 to the disturbing action of the major planets, and as this planetary 

 influence is sometimes sufficient, especially in the case of Jupiter and 

 Saturn, to change the direction of cometary motion, the great majority 

 of periodic comets should move in the same direction with the pla- 

 nets. Now, of the comets known to be elliptical, 70 per cent, have 

 direct motion. In this respect, therefore, theory and observation are 

 in striking harmony. 



2. When the relative positions of a comet and the disturbing 

 planet are such as to give the transformed orbit of the former a small 

 perihelion distance, the comet must return to the point at which it 

 received its greatest perturbation — in other words, to the orbit of 

 the planet. The aphelia of the comets of short period ought there- 

 fore to be found, for the most part, in the vicinity of the orbits of 

 the major planets. The actual distances of these aphelia are as 

 follows : — 



* Communicated by the Author, having been read before the American 

 Philosophical Society, November 19, 1869. 



