mi. J. H. JEANS OX THE DISTRIBUTION OF MOLECULAR ENERGY. 
4II 
auy way corresponds to the tacts, the molecules of these gases must possess a 
symmetry similar to that possessed by figures of revolution. 
PART 11. 
The Disteibgtiox of Energy tn a Gas of which the Molecules are of a 
MORE General Tyre. 
Statement of Problem to he Discussed. 
§ 17. Having discovered, by means of the simple dynamical illustration discussed 
in Part I., what sort of results are to he expected, it now becomes possible to examine 
the case in vdiich the molecules form a more complex dynamical system, and as this 
may be done by an entirely ditferent metliod from that previously followed, it is now 
possible to remove the restrictions which it was previously found necessary to impose 
on the nature of the molecules. 
The molecides are, as before, supposed to be all exactly similar, l)ut intermolecular 
forces are no longer excluded, and the radiation is supposed to be of a more general 
type. 
Let us su})pose that each molecule is a d 3 mamical system, possessing in itself 
k + n degrees of freedom in addition to the freedom of the molecule to move in 
space. There will therefore be 2 {Ic + n) + 3 co-ordinates required to specify tlie 
condition of a molecule apart from its position in space, and 4 [k -f n) -f- 8 quantities 
are required to specify a collision. 
The co-ordinates of position of any molecule will be 
X, II, z, the co-ordinates of its centre of gravity referred to axes fixed in space, 
Pu Pc’ • • • co-ordinates which do not occur in the expression for the 
potential energy ; as, for example, the co-ordinates which determine the 
, orientation of a rigid body. 
?q, r„, . . . the co-ordinates Avhich do occur in the ex})ression for the 
potential energy'. 
The co-ordinates of velocity will be 
iq, iq, iq the time-diflerentials of x, y, z. 
7i, p, • . • <ln ,, „ ,, Pi, ih, ■ • • P«. 
6q, q, . . . s^ ,, ,, ,, r^, . . . r^. 
We shall write c® for u~ + -p w~, and it will frequently be necessary, for the 
sake of brevity, to denote all co-ordinates of the same type liy a single representative 
letter without a suffix. 
Thus 
F(p) po, . . . p,) 
du — (/(q fpq cZiq, &c. 
