Chemistry and Physics. 239 
9. On the Viscosity of Gases at High Exhaustions.—In a 
paper read before the British Association in 1859, Maxwell pre- 
sented the remarkable theoretical result that the coefficient of 
the gas. Previ 
and Professor Crookes has lately investigated the subject, bring- 
ing to the study great experimental skill gained by for experi- 
ence in obtaining and measuring high exhaustions. For the 
was set in vibration by the radiometer effect on the semi-black- 
ened plate of mica), a careful analysis of the decrements of the 
Swings were necessary. Several curves illustrating the viscosity 
by means of this decrement in the swing are given; and a care- 
ful analysis on hydrodynamical principles by Professor G. G. 
Stokes is appended to Professor Crookes’ paper. The following 
Is a table of the results obtained by different observers. 
Graham. Kundt 
and Warburg. Maxwell. Crookes. 
ee Pa ae og ee 170000 1°0000 170000 170000 
12, ae ey ee 11099 “ “ 11185 
MORONS op ede 0-971 és “ O-9715 
Carbonic anhydride.._.. 0°807 0806 0-859 0°9208 
Carbonic oxide __._... 0°97 3 O-97T15 
Hydrogen ms eae Wie as 04855 0°488 05156 0°4439 
Professor Crookes believes that his results are more accurate 
than those of previous observers. e has obtained a much lower 
viscosity in the case of hydrogen and believes that its accurate 
obedience to Maxwell’s law is a proof of its purity, for any im- 
purity arising from admixture of other gases impairs the results. 
The results uphold Maxwell’s theory in general, and the more 
perfect the gas the nearer theagreement. Professor Stokes states 
cee his discussion of Professor Crookes’ results that the direct solu- 
tion of the problem of the movement of a lamina like a mica 
plate in even a perfect fluid cannot be solved; but theory enables 
One to compare the viscosities in different media under certain 
conditions of similarity. Professor Stokes is accordingly led to 
the following law. f 
ee If 
