410 TRANSACTIONS OF SECTION A. 
If the N resonators are to be in equilibrium with the external radiation they 
must absorb as much energy per second as they emit. The condition for equilibrium 
is therefore by (7) and (10) 
y? € 
Kv=3 7% : » » (il) 
e.~r—l 
Comparing this with Wien’s law in the form 
v3 v 
K,=", F(Z) . 25, OC Fit Santi 
we see that e« must be proportional to v. 
Putting 
C= Be 4a ei ys et es) 
we arrive at Planck’s law 
K ae : 7 (14) 
.Se Time he a se 
€ e7g—l 
os 
DEPARTMENT OF GENERAL PHYSICS. 
The following Papers were read :— 
1. The Law of Fall of a Drop through Air at Reduced Pressures and a 
Redetermination of e. By Professor R. A. MiuuiKan. 
A law of fall of the form . 
sage A Lil heme ae U 1 
eens yi+az} > ys a 
is found to hold accurately so long as 2 < ‘4, but beyond that limit it loses its 
applicability, and the term in brackets must be replaced by 
1 2 Pe 
{1+Al+ BET}. Ree 
i which A, B, and C are all positive constants. If 1 is obtained from the Boltzmann 
ormula 
p = ‘3502 mncl, 
then A is found to have the value 0°874, B the value 0°35, and C the value 1°7. 
The accurate evaluation of the constant A makes possible a determination of e 
which has a probable error of no more than one-tenth per cent. This value is 
e= 4775 x 10-° ES. Unit. 
2. On the Intensity of the Earth’s Penetrating Radiation over Land 
and Large Bodies of Water. By Professor J. C. McLennan. 
