142 Prof. 0. W. Richardson : 



field, if B/Ei= 10- 6 , this field should be equal to 2"13 X 10" 3 

 volt/em. 



We might also expect currents to be generated in a circuit 

 •of which part was falling under gravity relative to the rest. 

 I have made experiments to test this point. About 200 lb. 

 of mercury were allowed to fall in a continuous stream from 

 -a container through a short tube 9 mm. in diameter for a 

 distance of about a metre to a container at a lower level. 

 The containers were electrically connected by mercury-filled 

 glass tubes (to avoid thermoelectric disturbances) with a 

 galvanometer having a resistance of 600 ohms and a sensi- 

 tivity of 1 division for 2'6 X 10" 10 ampere. The resistance 

 of the rest of the circuit was negligible in comparison. No 

 deflexion amounting to a scale-division could be observed 

 when the mercury was running steadily. At the start and 

 finish rather irregular deflexions were observed, but there 

 are a number of ordinary explanations which might account 

 for them. However, I do not consider that these experi- 

 ments rule out the possibility of such effects at the start and 

 finish. In order to settle this point definitely more elaborate 

 apparatus would be required than I happened to have 

 available. 



On the view we are considering the force on an electron 

 in a gravitational field would be quite different from the 

 ordinary Newtonian attraction on its mass. The accelera- 

 tion of an electron in the earth's gravitational field, for. 

 example, would be about 10 12 cm. sec." 2 . A correlated 

 effect is that the apparent weight of equal electric charges 

 should, to a very close approximation, change sign with the 

 sign of the charge. (The approximation neglects the gravi- 

 tational term in B, which is about 10 " 10 of the whole.) This 

 can be tested by placing a very light earth-connected plate 

 in a median position in a flat insulated metal box and finding 

 if the apparent weight of the plate varies with the sign of 

 the charge on the box. Very careful experiments on this 

 principle have been made in the Wheatstone Laboratory by 

 Dr. L. Simon?, and as the result is important they are 

 described in the appendix. Dr. Simons finds no displace- 

 ment, although he concludes that he could have detected a 

 deflexion equal to about one-third of that to be expected if 

 B = 10- 6 E,. 



The charges which would develop on a conducting sphere 

 of gravitating matter are apparently much too small to account 

 for the earth's magnetic field. I find that the equations are 

 solved by an electric distribution of uniform volume density 

 .throughout the sphere, and if the sphere is uncharged an 



