186 Trans. Acad. Sct. of St. Louis. 
enclosed in a glass case containing drying material, and 
it was driven by a single-phase motor. Placing the large 
masses in the position shown in Fig. 3 at the time when 
the work to be described began, increased the scale read- 
ing by 0.40 em. 
An illustration of the results obtained is shown in 
Plate XLV. In each case the masses had been grounded 
during the preceding night. The scale was displaced in 
order that the two diagrams might be shown on the same 
plate, without interference. On the lower diagram the 
arrangement of apparatus was as shown in Fig. 3. The 
hour of the day is laid off upon the horizontal axis. The 
scale reading in em. is along the vertical axis. One mm. 
represents an angle of 2.6 minutes of are. The negative 
terminal was applied at 9:38 a.m. On the diagram the 
arrow indicates the time. At 10:12 a. m. the terminals 
were reversed, an operation which required a few sec- 
onds of time. At 11:30 the machine was disconnected. 
There was evidence shown in the drop in the reading at 
11:20 that the reading would begin to decrease. The up- 
per diagram of this plate shows results obtained on May 
4. Here the positive terminal was first applied at 9:35 
a.m. The terminals were reversed at 10:24 and the ma- 
chine was stopped at 11 :20, the readings being con- 
tinued to 12:05 p.m. In this work the conductors upon 
which the 800 pins were supported were directly con- 
nected with the large masses and shield. 
When direct contact was made between the pin-con- 
ductors and the large masses, the changes took place more 
rapidly than when the air surrounding the masses was 
supercharged with negative corpuscles emitted from the 
pin points, or when the reverse action took place, this 
alone being depended upon to change the potential of the 
masses. The most interesting feature of this work is the 
complete elimination of the possibility that the apparent 
decrease in the attraction between these masses was due 
to the convection currents of air resulting from heat ef- 
fects, Reversing the terminals would not reverse these 
heat effects. 
