384 Trans. Acad. Sci. of St. Louis. 
electrically charged by means of a wire armed with a pin 
which was thrust through a glass tube which was thrust 
through the end of the shield about an inch above the level 
of the suspended masses, and was sealed in place. The 
inner end of the tube was drawn to a small diameter, 
being only large enough to admit the end of the pin. This 
could be withdrawn at any time and the outer end of the 
tube could be covered with a metal tube which was closed 
with a metal plug at its outer end. 
Convection effects, due to changes in temperature, 
have been very carefully studied. When the masses have 
not been electrically charged for several days, the rise 
in the temperature of the room during the day caused a 
very slow increase in the seale reading which determined 
the position of the suspended masses. This change in 
position decreases the distance between the suspended 
masses and the large masses. When a door opening into 
the hallway was opened for four minutes this change is 
larger and more abrupt. When an outside window was 
opened, admitting cold air, a sudden decrease in the read- 
ing results. 
The room containing the apparatus was always entered 
from an adjoining room, from which heat from the heat- 
ing system was wholly cut off. 
In order to decrease convection effects, the large masses 
and shield were covered on all sides with a pile of cotton 
batting, forming a layer of about six to eight inches in 
thickness. This was permissible by reason of the fact 
that the electric machine in the adjoining room was dis- 
carded as a source of electricity. It was replaced by the 
earth, which had been found to be equally effective, and 
which has a much greater capacity. The large masses 
and shield, and when necessary, the injection pin were 
connected by wire with a copper lightning rod on the out- 
side of the building. This rod formed the ground con- 
nection for a steel tower used for wireless. Its top was 
one hundred feet above the ground. This tower is 
mounted upon the roof of the physies building, the walls 
