Nipher — Gravitational Repulsion. 179 



closed by a cylinder of copper wire gauze, between which 

 and the outer screen was very loosely packed cotton 

 fiber. A thin layer of cotton was placed at the ends of 

 the screen, being also held in place by wire netting. This 

 was designed to diminish convection effects. 



The body of the observer was wholly below the level 

 of the table. Radiation of heat from the head to the 

 screen was cut off by sheets of heavy cardboard. 



The two rooms used for this work were wholly discon- 

 nected from the heating system of the building. During 

 the day the temperature of the large masses was usually 

 slightly lower than that of the shield around the sus- 

 pended masses. This temperature difference never ex- 

 ceeded 1°.5 C. 



The large masses were placed at the ends of the 

 screen or shield in line with the rod upon which the small 

 masses were mounted, in order to determine their effect 

 upon the time of vibration of this bifilar pendulum. The 

 large masses and screen were in direct metallic connec- 

 tion, and the air around them was electrified by a dis- 

 charge from pin-points. A disc armed with 150 pins was 

 placed with the pin-points 4 cm. from each of the large 

 masses. A noiseless discharge was delivered from the 

 points of the pins. 



Let T represent the time of vibration when the masses 

 were away. 



Let T x represent the time of vibration when the masses 

 are in place. 



Let To — the time when the masses and screen are elec- 

 trified. 



Then 



T=2tt ■ 



4 



(P 



mg T 



(1) 



Here m is the suspended mass, 2d the distance between 

 the two silk fibers on which it is suspended, and I their 

 length. I is the moment of inertia. 



