of the Weight of a Body on its state of Electrification. 871 



4. Small permanent fields inside the balance case. The 

 remarks under 1. above apply to this case also. In order to test 

 directly Experiment 10 was tried, in which a small field was pur- 

 posely introduced. The small effect recorded is within the limits 

 of experimental error, as an examination of the actual observations 

 will shew. Asa matter of fact, no movement whatever of the scale 

 could be detected when the field was put in or out. 



5. Surface effects of the pieces carrying the induced charges. 

 In Experiment 9 one of the end pieces was coated (except near 

 the edges) with shellac, and this end of the apparatus only was 

 charged. It was feared that the shellac might give rise to electro- 

 static difficulties, but none were experienced, thanks no doubt to 

 the approximate symmetry of the apparatus. It is probable that 

 the field plate was a little further from the beam than usual in 

 this experiment. The result was the same as in Experiment 7 B, 

 when the same side of the apparatus was used. The value in 

 Experiment 9 is probably a little low (perhaps 1 in 5 or 6) due to 

 the suspected increase in the distance between the plates, but 

 the similarity of the results shews that these are not caused by 

 any peculiar action of the metal surfaces. 



Some other sources of error, such as heating and electro- 

 magnetic effects, have already been dealt with. 



(4) Conclusion. 



Whether the effect be due to a modification of gravity or not, 

 the experiments appear to shew that a body, positively charged 

 with 20 electrostatic units of electricity, behaves as though it were 

 heavier than the same body negatively charged, by an amount of 

 the order of "0007 mgms. If the effect be due to a change in 

 gravity, there will exist in an electrostatic field a small amount of 

 energy due to this cause, and this will involve a very slight 

 alteration in the configuration of the lines of force from that given 

 by ordinary electrostatic laws. This would be so small as to pass 

 unnoticed in ordinary cases. It would be such that with given 

 conductors charged in a given way and then reversed as to sign of 

 charge, we should obtain two slightly different configurations of 

 field. Delicate instruments might detect this, and it is possible 

 that the different zeros of a quadrant electrometer, with the needle 

 positively and negatively charged, and quadrants earthed, may be 

 due to this cause, though the writer has not investigated these 

 effects, for the explanation of which the above suggestion may be 

 quite inadequate. 



It was suggested to the writer that the effects might possibly 

 be caused by an accumulation of air condensed on the surfaces 

 of the metal, the quantity being greater when the surface was 

 positively than when negatively charged. Experiment 9 was 



