NEW EVIDENCE OF A RELATION BETWEEN 

 GRAVITATION AND ELECTRICAL ACTION, 

 AND OF LOCAL CHANGES IN THE ELEC- 

 TRICAL POTENTIAL OF THE EARTH.* 



Francis E. Nipher. 



In the work to be here described, the apparatus used 

 was a modified form of that used by Cavendish, as shown 

 in the former paper, published by the Academy of Science 

 of St. Louis, Vol. XXIII, pp. 183-4-5. 



The wood frame was in this case covered with tin-foil, 

 within and without. The sheet metal forming the sides of 

 the shield were clamped to the wood frame, by bars of 

 wood which were also covered with tin-foil. All joints 

 were sealed with wax before the tin-foil was put in place. 

 The whole shield was then surrounded by two end caps 

 of metal which meet at the middle of the shield and are 

 sealed together by means of tin-foil. A layer of air was 

 thus formed between the two metal shields surrounding 

 the suspended masses. Either of these two metal shields 

 was considered ample protection to prevent the sus- 

 pended masses from being acted upon electrically by the 

 large masses. The layer of air between the two shields 

 was designed to diminish convection effects within the 

 shield due to changes in the temperature of the room, 

 and changes in the temperature of the air within the 

 room were made as small as possible, by cutting off all 

 sources of artificial heat. It did not usually vary more 

 than 1.5 degrees C. during the day. The temperature 

 was determined by means of a thermometer placed near 

 the large masses. The reading was by means of a tele- 

 scope. The reading could be made accurately to tenths 

 of a degree C. and hundredths of a degree could be esti- 

 mated with fair precision. The air within the shield was 



(383) 



