ON THE SUN'S HE A T. 405- 



to let the sun have his present slow rotation 

 when shrunk to his present dimensions. This 

 exceedingly exact aiming of the one body at 

 the other, so to speak, is, on the dry theory of 

 probability, exceedingly improbable. On the 

 other hand, there is certainty that the two bodies 

 A and B, at rest in space, if left to themselves 

 undisturbed by other bodies and only influenced 

 by their mutual gravitation, shall collide with 

 direct impact, and therefore with no motion of 

 their centre of inertia, and no rotational momentum 

 of the compound body after the collision. Thus 

 we see that the dry probability of collision between 

 two neighbours of a vast number of mutually 

 attracting bodies widely scattered through space 

 is much greater if the bodies be all given at rest, 



wrote Latin) to signify translational importance of motion. Moment 

 of a couple, moment of a magnet, moment of inertia, moment of 

 force round an axis, moment of momentum round an axis, and 

 corresponding verbal combinations in French and German, are 

 expressions which have been introduced within the last sixty years 

 (by scientists speaking, as now, each his own vernacular) to signify 

 the importance of the special subject referred to in each case. The 

 expression "moment of momentum" is highly valuable and con- 

 venient in dynamical science, and it constitutes a curious philological 

 monument of scientific history. 



