294 



SCIENCE 



[N. S. Vol. XL VI. No. 1186 



directly connected with the shield and the 

 large masses if a rapid change was desired. 



When either the positive or the negative 

 terminal of the machine was applied, the 

 attraction of the large masses for the sus- 

 pended masses was diminished. It sometimes 

 happened that a slight increase was shown at 

 first, until a condition of zero potential was 

 reached. This was only observed when direct 

 contact of the masses with the 800 pins was 

 not made. It then required several hours for 

 the decrease in gravitational attraction to 

 reach a limit. Then when the other terminal 

 was applied the masses slowly returned to 

 the original position. If this deiiection were 

 due to heat effects causing convection cur- 

 rents of air within the shield, this return mo- 

 tion due to change in terminals would not 

 occur. 



On the occasion when the most marked 

 effects were obtained, the decreasing effect 

 took place very slowly, requiring five hours. 

 There was no direct contact between the large 

 masses and the 800 pins. The positive ter- 

 minal had been applied. I^egative electrons 

 were being drained from the air surroundiing 

 the large masses and from the outer surface 

 of these masses. Gravitational attraction had 

 been reduced to zero. The negative terminal 

 was then applied, and the masses were directly 

 connected with the pin conductors by means 

 of a metal rod. In five minutes (the time of 

 a semi-vibration) the suspended masses had 

 swayed back about half the angle over which 

 they had slowly moved in the previous five 

 hours. They then swayed back and oscillated 

 to and fro, the mean of the extreme readings 

 representing a decrease of 250 per cent, in the 

 normal value of gravitational attraction be- 

 tween the masses. The arc of vibration 

 during the next forty minutes was about equal 

 to that due to normal attraction between the 

 masses. 



On the next morning the suspended masses 

 were at rest, in a position which indicated that 

 the large masses still repelled the suspended 

 masses with a force about 2.5 times that of 

 gravitational attraction. This position re- 

 mained constant for two hours. The positive 

 terminal was then applied and direct contact 



was made between the masses and the 800 pin 

 conductors. During the nest eighteen min- 

 utes the suspended masses swayed over an arc 

 very nearly equal to that due to normal attrac- 

 tion. The attraction between the masses was 

 increased. During the next twelve minutes 

 they swayed backward over an arc about twice 

 as great. The condition of zero potential had 

 been passed. The force steadily decreased 

 during the following ninety minutes. The 

 gravitational attraction had then decreased to 

 more than 300 per cent, of its maximum value. 

 The negative terminal was then applied, and 

 in two hours the reading was that at the be- 

 ginning of the work of the previous day. 



It is not necessary to continue an experi- 

 ment of this kind throughout an entire day. 

 Either terminal may be applied when the sus- 

 pended masses are at rest, until an appreci- 

 able decrease in the gravitational attraction 

 has become evident. A reversal of contacts 

 of the machine may then be made and the 

 masses will slowly sway back to their original 

 position. This operation requires less than 

 one hour. The evidence is as convincing as 

 that produced by a feeble current of electricity 

 upon a magnet suspended above it. 



ISTo attempt has been made in this work to 

 obtain precise results. The aim has been to 

 determine whether it would be proper to con- 

 struct the much more expensive apparatus 

 which will be needed, and which will permit 

 the independent electrification of the sus- 

 pended masses. Some results which have been 

 obtained have aroused the suspicion that the 

 " charges " on these masses varies from day 

 to day, and that when their potential due to 

 these charges is zero absolute, the electrifica- 

 tion of the large masses will have no effect 

 upon gravitational attraction. A modifica- 

 tion of the apparatus used by Boys will be re- 

 quired. 



The work here described has been done in 

 a private laboratory in the second story of 

 Ead's Hall, now occupied by the physics de- 

 partment of Washington University. 



lly thanks are due to the Carnegie Institu- 

 tion of Washington, for financial aid in this 

 work. 



Francis E. I^ipher 



