THE VISCOSITY OF GASES

253

If v is the velocity of a droplet of w, density p the

action of gravity alone, and 1*1 Its Telocity the in-

fluence of the electrical field whose strength is X in
units 3 then

i; ma

- = J^T+TY^ (ios;

Applying Stokes' Law, Eq. (62), to the
Is 47rT1/3, we obtain

6 = I 3 (§)?2 ":7r?:) r* (109!

A beautiful application of this method has by

Millikan (I9O9, etc.)- He has found the most
for e to be 4.69 X lO"10. This leads to the number
in a gram molecule N = 6.18 X 1023 and the of the

gen atom as 1.62 X 10-24 g.

Chapman (1916) and Rankine (1920-1) have the

diameters of the atoms of the monatomie from

tions of the viscosity. They regard the atoms as
having the well-defined absolute diameters given below.

ATOMIC DIAMETERS OP SOME OF THE NOBLE GASES

Gas
Viscosity
i Crystal

Jsfeon . .........
2 35 X 10"1
i
! 61 30 X I0~s

•AjTsron
2 87 X 1CT1
1 2 05 X 10"1

Ivrypton. . .............
3.19 X lO"1
i 2 35 X if)""1

!2£!eno& ..........
3.51 X ICT1
j 62 70 X id™1

These values agree very well with those obtained
der Waal's equation but they are somewhat greater the
diameters of the outer electron shells of the atoms as
by Bragg from his crystal measurements.