IS THE ORGANISM A MECHANISM? 651 



postulate any past duration, however great. Now there appears, 

 to be only one way out from this deadlock ; somewhere or other 

 in the universe there must be a restoration of available energy. 

 This is the explanation suggested by Boltzmann, and we may 

 usefully consider it here, since it suggests at once a manner of 

 regarding the activities of the organism which indicates that a 

 theory of life may, after all, be possible. 



Let us consider, then, a volume of a " perfect " gas equal to, 

 say, one-tenth of a litre. Let this gas be contained in a vessel 

 made of some perfectly non-conducting material, and let the 

 vessel have a partition, also made of non-conducting material, 

 dividing it into two chambers. Let the gas in the two chambers 

 be at unequal temperatures, T? and T% } T° being greater than T°. 

 Now let the partition be withdrawn so that the gases mix. In a 

 few minutes thermal equilibrium will be established and the 

 temperature of the moisture will be, everywhere, sensibly 

 the same. 



A perfect gas consists of a very large number of molecules 

 moving in straight lines at very high velocities. These molecules 

 incessantly collide with each other, and since they are perfectly 

 elastic no energy is lost in the collisions. They must be moving 

 in every conceivable direction and (within a certain range) at 

 different velocities. But there is, at a definite temperature and 

 pressure, a certain mean molecular velocity towards which the 

 greater number of the molecules approximate. Some are moving 

 at higher, and others at lower velocities than the mean one, and 

 these velocities other than the mean deviate from the latter in 

 such a way that they can be represented by a " frequency dis- 

 tribution " with the mode at the mean. For two gases differing 

 only in their temperature the squares of the mean velocities 

 are proportional to the absolute temperatures, that is, V\ : VI = 

 T°:TS. 



Since the molecules of the gas are moving with different 

 velocities, and in every conceivable direction, the result of their 

 collisions must be that molecules moving with speeds above the 

 mean will tend, owing to collisions with molecules moving with 

 speeds below the mean, to lose some of their velocity. When 

 the two gases at different temperatures are allowed to mix the 

 molecules of the hotter one will communicate to the molecules 

 of the cooler one some of their velocity of movement. Thus the 

 temperature of the cooler gas must increase while that of the 



