The Kinetic Theory of Gases. 467 
t : 6 
typical case was found experimentally to be a of the 
distance between two principal maxima; ?.e. the adjacent 
secondary maxima are lost in the principal maxima. 
The observations recorded in this paper were made in the 
Physical Laboratory of the University of Glasgow with 
Prof. A. Gray’s echelon spectroscope, and I have to thank 
Prof. Gray both for encouragement and advice. 

LVI. Note on Mr. Jeans’ Letter in Phil. Mag. for December. vi 
To the Editors of the Philosophical Magazine. y 
GENTLEMEN,— / 
: : : : f 
Mr. JEANS in his letter omits to take notice of the most 
important point which arises on his paper and my note.“ He 
claims, namely, to have proved Maxwell’s law, which may 
be stated as follows. If m, ... m, be the masses of n 
molecules, forming a group out of the much greater number 
N, uw, vy w, &e. their velocities, 7, y, 2, Uc. their space 
coordinates, then the chance that these velocities and 
coordinates respectively shall lie within assigned limits 
me . wm +duy~.~~ke., 2 . . 2, +d, Xe. is proportional to 

e—MSm(u? +074 w?) ~ 2x) du ee « dw, da; 7. 26 @ dzn, 
where y denotes the potential of external forces which in 
that configuration the molecules have. Intermolecular 
forces are not considered. 
But this expression may be put in the form 
Flu) f (oF om). » «f(a F (2X); 
in that form it asserts that ‘“‘the chance of the velocities 
of any molecule, as m,, lying within assigned limits. is 
independent ot the positions and velocities of all the other 
molecules for the time being.” 
Maxwell’s law cannot then be true unless at the same time 
that statement is true, and that statement I call assumption A. 
But Mr. Jeans has proved that this assumption is untrue in 
fact—namely, in paragraph 2 of his paper he points out that 
it is inconsistent with the continuity of the motion (and is 
therefore untrue because the motion is continuous), and in 
his letter he says “the laws of dynamics imply causation 
with no greater certainty than they imply the negation of 
assumption A.” If, then, Maxwell’s law cannot be true 
without A being true, and A is not true, it necessarily follows 
that Maxwell’s law is not true. 

