BicKERTON. — On the Genesis of Worlds and Systems. 191 



hypothesis I am about to deacribe suggests that this is the case, but espe- 

 cially says further, that if they do knock against each other the blow may 

 be a mere graze of the two outsides, or sometimes a large piece of each may 

 be struck off, and in extremely rare cases they may meet fair ; but as this 

 latter is so extremely rare, the other cases are those chiefly considered, and 

 so the theory is called Partial Impact. I shall now try and show you what 

 a perfect Aladdin's lamp of possibilities this theory possesses. 



A gentleman who was present at a bombardment told me that he had 

 seen the cannon balls strike pieces off the cannon and travel on in space. 

 But the energy of each particle of a star at collision is hundreds of thou- 

 sands of times greater than in a cannon ball, so the stars also will strike a 

 piece off each where they strike one another, the remainder passing on in 

 space. The proportional resistance to motion produced by impact in the 

 escaping parts, would be thousands of times less than if a cannon ball of 

 butter just grazed the top of an u*on wall ; in fact, the large pieces not 

 coming into collision will be certaia to travel on. So the effect of the col- 

 lision of om* two stars will be to strike a piece off each other where they 

 touch each other, and each star will travel on, with a slice cut off its 

 side. The parts of each which met will be left behind by both the retreat- 

 ing bodies, and will probably remain where the collision occurred. But, 

 owing to the way it has been struck off, the two sides being impelled in 

 opposite directions, it cannot help revolvuig, and it is not unlikely that 

 nearly all the thousands of rotating bodies and systems in the Universe may 

 have thus been set spinning by partial impact. At least, although we do 

 not know what other agencies may ultimately be found to be capable of 

 producing rotation, at present indh-ect impact seems to be the only one 

 known. 



Everyone, now-a-days, knows that heat is a kind of motion, and that 

 ordinary motion destroyed, produces heat. An axle, screw, or gimblet— 

 without grease — gets hot if quickly used. A rifle bullet makes a flash ol 

 light on striking ,the target, and often melts. A particle of matter plunges 

 into oiu- atmosphere and becomes so hot that it forms a shooting star. A 

 school-boy takes his caning, and speaks of it as a warming. We rub the 

 little cold hands of the wee ones who have been playing with the snow, and 

 we stamp our feet when the thermometer sinks below zero. So if staz&, 

 come into collision they will develope heat in the part struck off as striking 

 a flint and steel strikes off a spark. In fact, our two stars may be con- 

 sidered as flint and steel meeting one another, striking off a spark, and 

 passing on in space. Any student of heat will tell you that if the motion 

 of a piece of iron be destroyed, he can calculate the temperature produced, 

 if he knows its speed, and that the heat does not depend on the size of the 



