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 could be withdrawn at any time and the outer end of the 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 scale 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 physics building, the walls 



