82 
LUMMER. 
S k T 5 — constant 
(3) 
o _ ch l 
^5 ch 
(4) 
where S\ denotes the energy of the black radiation with respect 
to the spectral region dA between wave lengths A and A + dA, and 
T the absolute temperature, and where the constants are: 
a — 7.061 X 10 15 erg / cm 8 , degree . 
b = 0.294 cm, degree. 
h = 6.548 X 10 ~~ 27 erg, sec . 
k = 1.346 x 10 erg / degree. 
c == 3 X 10 10 cm/ sec. 
From these quantities we can, as a first application, calcu- 
late according to Planck's ingenious theory which leads to 
the spectral-equation (4), the number of atoms of an 
ideal gas in 1 cubic centimeter at 0° Centigrade and atmos- 
pheric pressure, N = 2.76 X 10 19 . 
Since one mole carries the electric charge of 96,580 cou- 
lombs or 96,580 X 3 X 10 9 electrostatic units, and since one 
mole has N molecules, the electric charge on one single 
molecule is 4.5 X 10 “ 10 electrostatic units. Using also the 
constant of gravity 
/ = 6.69 X 10 ~ 8 cm* / gr. sec 
and the velocity of light 
c = 3 x 10 l ° cm / sec 
we obtain according to Planck the “natural units” of length, 
mass, time, and temperature by equating the above constants 
to unity : 
