ON THE SUN'S HEAT. 407 



outward from the line of the motion before the 

 collision, and swelling to a bulk several times 

 greater than the sum of the original bulks of the 

 two globes. 1 How far the fluid mass will fly out 

 all round from the line of collision it is impossible 

 to say. The motion is too complicated to be 

 fully investigated by any known mathematical 

 method ; but with sufficient patience a mathe- 

 matician might be able to calculate it with some 

 fair approximation to the truth. The distance 

 reached by the extreme circular fringe of the 

 fluid mass would probably be much less than the 

 distance fallen by each globe before the collision, 

 because the translational motion of the molecules 

 constituting the heat into which the whole energy 



1 Such incidents seem to happen occasionally in the universe. 

 Laplace says " Some stars have suddenly appeared, and then 

 disappeared, after having shone for several months with the most 

 brilliant splendour. Such was the star observed by Tycho Brahe in 

 the year 1572, in the constellation Cassiopeia. In a short time it 

 surpassed the most brilliant stars, and even Jupiter itself. Its light 

 then waned away, and finally disappeared sixteen months after its 

 discovery. Its colour underwent several changes ; it was at first of 

 a brilliant white, then of a reddish yellow, and finally of a lead- 

 coloured white, like to Saturn." (Harte's translation of Laplace's 

 System of the World. Dublin, 1830.) 



