50 KANTS UNIVERSAL NATURAL HISTORY 



of the distance. This is the reason why the central 

 force, so often mentioned, is also called gravity. 



And, moreover, it is in the highest degree probable 

 that if an action takes place only in the presence of a 

 certain body and in the proportion of its proximity, and 

 if the direction of it is also to be referred most exactly 

 to this body, it must be believed that this body is in 

 some way or other the cause ^of that action; and hence 

 it is held that there is sufficient reason for ascribing this 

 universal falling of the planets towards the sun to a 

 Force of Attraction in the sun, and to attribute this 

 same power of attraction to all the heavenly bodies. 



When a body, therefore, is freely abandoned to this 

 influence, which impels it to sink towards the sun or 

 to a certain planet, it will fall to it in a constantly 

 accelerated motion, and at last will unite with its mass. 

 But if it has obtained an impetus sideways, and if this 

 is not so powerful as to form an exact equilibrium with 

 the falling force, it will fall in a curved movement 

 towards the central body. And if the impulsion which 

 has been impressed upon it, has been at least strong 

 enough before it comes in contact with the surface of 

 the central body to remove it from the perpendicular 

 line by half the diameter of the body in the centre, it 

 will not reach its surface; but after it has swung itself 

 close round it, by the velocity acquired in falling, it 

 will again raise itself as high as it had fallen, then to 

 continue its revolution in a constant circular movement 

 round it. 



The difference between the orbits of the comets and 

 the planets, thus consists in the balancing of the lateral 

 movement with the pressure which impels them to fall : 



