Nipher—Gravitation and Electrical Action. 173 
The large masses were then wholly enclosed in two 
metal boxes, from which the masses were insulated. The 
masses rested upon rubber blocks placed upon the bot- 
tom of the boxes, and each box was mounted upon rubber 
blocks which rested upon plates of glass. The masses 
were in the same position as in the work above described. 
The boxes were separated from the shield, enclosing the 
suspended masses, by the plates of glass and the asbes- 
tos paper. 
The two metal boxes and the metal shield were then 
electrified precisely as has been done before. It was then 
found impossible to increase the are of vibration of the 
suspended masses, although the operation was continued 
for several hours. If the former results had been due to 
heat effects, they should have produced the same results 
in this case. The large masses were removed from the 
enclosing boxes. The empty boxes and screen were then 
electrified as before. 
No change in the amplitude of vibration could be pro- 
duced. 
These results seem to indicate clearly that gravita- 
tional attraction between masses of matter depends upon 
their electrical potential due to electrical charges upon 
them. To assume a special case, such as exists when the 
gravitation constant is being determined, Newton’s law 
holds only when the common potential of the two bodies 
is such that their gravitational attraction for each other 
is a maximum. If the two masses are not separated by 
a metal shield and their common potential is that of the 
earth, these masses will repel each other by a force rep- 
resented by the final term in Eq. (1) and the value of K 
will also be diminished, if the above conclusions are cor- 
rect. If the two masses are separated by a metal shield, 
this final term will be eliminated, but the value of K will 
be diminished and may seem to be variable, if there are 
local variations in the potential of the earth. By adjust- 
ing the potential of the attracting masses by well known 
means we may hope that the real value of K and the 
