72 SCIENCE AND METHOD. 



of chaos in unstable equilibrium, and the whole of 

 nature would appear to him to be given up to chance. 



IV. 



We come now to other arguments, in which we 

 shall see somewhat different characteristics appearing, 

 and first let us take the kinetic theory of gases. How 

 are we to picture a receptacle full of gas ? Innumer- 

 able molecules, animated with great velocities, course 

 through the receptacle in all directions ; every moment 

 they collide with the sides or else with one another, 

 and these collisions take place under the most varied 

 conditions. What strikes us most in this case is not 

 the smallness of the causes, but their complexity. 

 And yet the former element is still found here, and 

 plays an important part. If a molecule deviated 

 from its trajectory to left or right in a very small 

 degree as compared with the radius of action of the 

 gaseous molecules, it would avoid a collision, or would 

 suffer it under different conditions, and that would 

 alter the direction of its velocity after the collision 

 perhaps by 90 or 180 degrees. 



That is not all. It is enough, as we have just seen, 

 that the molecule should deviate before the collision 

 in an infinitely small degree, to make it deviate after 

 the collision in a finite degree. Then, if the molecule 

 suffers two successive collisions, it is enough that it 

 .should deviate before the first collision in a degree of 

 infinite smallness of the second order, to make it deviate 

 after the first collision in a degree of infinite small- 

 ness of the first order, and after the second collision 

 in a finite degree. And the molecule will not suffer 

 two collisions only, but a great number each second. 



