ORIGIN OF KOTAEY MOTION. 75 



latter ball. But there are a great many chances against both 

 balls striking in such a line, and if we suppose a constant stream 

 of balls (corresponding to particles) flowing inward toward the 

 central ball, the probability of the latter being soon struck a 

 little out of the line of its center, would amount to an almost 

 absolute certainty. In case this should happen, a rotary mo- 

 tion of the central body would necessarily take place as a re- 

 sult of the momentum of the body or bodies impinging upon 

 it, especially if the latter bodies, as a result of magnetic or 

 other attraction, attach themselves permanently to the surface 

 of the former while still under the influence of this mo- 

 mentum. 



Suppose, then, there is a constant stream of bodies flowing 

 inward from all directions toward the central body, as is sup- 

 posed to be the case with particles of nebulous matter flowing 

 inward toward a common center ; the rotation of the central 

 mass itself when once established, will, by the friction of its 

 revolving atmosphere, if from no other cause, be sufficient to 

 throw the approaching end of every radial line of gravitating 

 particles out in the same direction from its center, and thus the 

 momentum of every impinging particle will add to the ten- 

 dency to central rotation. As the particles gradually estab- 

 lish relations with each other, through their various degrees 

 of attenuation from center to circumference, rotation will 

 gradually be established throughout the whole mass, the mo- 

 tion being relatively swift at the center, and gradually grow- 

 ing slower at every remove toward the circumference, where 

 it is the slowest. 



The idea has been illustrated by a reference to the effect 

 produced by different currents of water flowing toward a com- 

 mon center, which effect is well known to be that of a whirl, 

 rapid at the point of meeting, and growing more tardy at 



