162 
IOWA ACADEMY OF SCIENCE 
the temperature was brought to 23®C, when good clouds were again obtained. 
After that the temperature of the room was taken with each series of observa- 
tions. Owing to space the complete data for only two determinations are given 
to show how they ran: 
Field 2,400 volts=16 E. S. 
Vo=.0387 cm. 
Vi=.0497 cm. 
Temp.=26°C 
e=4.1X10-"'' 
Field 2,950 volts=19.67 E. S. 
Vo=.0387 cm. 
Vf=.053 cm. 
Temp.=26°C 
e=4.25X10-"‘' 
Field off 
Field on 
Field off 
Field on 
5.4 secs. 
4.0 secs. 
5.2 
4.0 
5.2 
3.8 
5.2 
4.0 
4.8 
■ 3.8 
5.0 
3.8 
4.8 
3.6 
5.0 
4.4 
5.2 
4.0 
5.4 
4.0 
5.6 
4.0 
5.2 
4.0 
5.6 
4.0 
4.8 
4.2 
4.8 
3.2 
5.4 
4.4 
5.2 
4.0 
5.2 
3.6 
5.2 
4.0 
5.2 
4.0 
5.2 
3.6 
5.2 
4.0 
5.2 
3.6 
5.0 
3.8 
5.2 
3.6 
Mean 5.17 
4.02 
Mean 5.17 
3.77 
Summary: 
3.81X10-^° 
3.89 
4.34 
3.66 
4.10 
3.94 
4.37 
3.84 
Mean 4.03X10-^° E. S. Units 
Since the charge of the hydrogen atom is the same as the negative ion, the 
above determination gives on computation a mass of 1.3x10-^^ for an atom of 
hydrogen and a mass of 2.6x10-^^, for a molecule or hydrogen. Taking the mass 
of a cubic centimeter of hydrogen at 0®C. and 760 mm. as 9x10-^ grams we get 
for N the number of molecules per cubic centimeter, 3.4x10-^®. This is lower 
than Wilson’s or Thomson’s determination, but nearer the best estimates ac- 
cording to the kinetic theory of gases, which I find to be as low as 2.1x10-^®. 
