BY G. R. SM ALLEY, ESQ. 331 



interest, but an undue disposition to connect them with certain 

 terrestrial events. 



These ephemeral bodies, of which probably there are a vast 

 number which we never see, follow the same rule as that 

 observed in all other Planetary bodies, that is, they move in the 

 geometrical curve which we call a conic section. This is a mere 

 problem in geometry, for when we have obtained by observation, 

 the co-ordinates of a body's path generally from the right 

 ascension and declination we can lay down the form of that 

 path, and identify it, much in the same sort of way as we may 

 lay down upon a map and identify the track of a traveller, from 

 his observed latitudes and longitudes. Of these curves, some 

 of the Comets select the ellipse, or oval, more or less elongated, 

 in which case the return may be predicted. Some few have been 

 suspected though with no degree of certainty of moving in 

 hyperbolic paths ; whilst the greater number appear to move in 

 parabolas (the path of the common projectile), a curve which 

 forms a sort of connecting link between the ellipse on one side, 

 and the hyperbola on the other ; in such cases as the two 

 last, the return of the Comet cannot be anticipated. 



Now, without pausing to comment upon the remarkable cir- 

 cumstance of nature selecting for her operations those curves 

 which are exhibited by dividing a cone in different directions, I 

 will merely remind you how Newton demonstrated that, if a body 

 be projected in space, and acted upon continually by a force which 

 varies inversely as the square of the distance, and resides in a 

 fixed centre, that body will describe one of " the Conic Sections," 

 the centre of force being in the focus. Conversely, if we find 

 from Geometrical considerations, that a body describes one of 

 the conic sections about a centre of force situated in the focus, 

 we are sure that the Law of Force is that of the inverse square 

 of the distance. 



Now, observation shows that Comets do move in conic sections, 

 and that the Sun resides in the focus. Hence it follows that 

 Comets necessarily follow the Law of Gravitation. Moreover, there 

 must be a certain amount of substance about them, however 

 attenuated that substance may be otherwise they could not be 

 subjected to the Laws of Gravitation. Again, admitting the 



