414 



SCIENCE 



[N. S. Vol. XLIII. No. 1108 



tual induction. If insulated wliile in this 

 position and then separated, the whole or a 

 portion of their bound charges become free 

 charges. If while separated they are elec- 

 trically connected with the earth, such a trans- 

 ference of electricity will take place between 

 each of them and the earth as will restore 

 their original fixed charges. 



Since a metal within a hollow conductor of 

 another metal is wholly within the field of in- 

 duction of the outer metal, the fixed charge 

 which the inner metal will take when in con- 

 tact with the outer will be determined to the 

 greatest possible extent by the bound charge 

 induced by the outer metal. Accordingly, this 

 will, in general, be different from the fixed 

 charge which the inner metal will take in the 

 earth's field alone. It follows from this that 

 when two metals inside a hollow conductor are 

 brought into contact with each other and with 

 the outer hollow conductor, the bound charges 

 which they acquire are partly due to their 

 mutual induction and partly to the induction 

 of the outer hollow conductor. If they are 

 flat plates and are placed parallel and very 

 close together when touched to the outer con- 

 ductor, their bound charges may be quite 

 largely due to their mutual induction; if they 

 are spheres with their surfaces touching while 

 they are put into contact with the outer con- 

 ductor, their bound charges will be determined 

 principally by the induction of the outer con- 

 ductor. 



Thus, a zinc baU about 5 centimeters in 

 diameter was insulated by a silk thread and 

 was lowered into a metal beaker of 750 c.c. 

 capacity until it touched the bottom. It then 

 held the fixed charge due to the induction of 

 the surrounding beaker. When it was lifted 

 out of the beaker, this charge became free, and 

 could be shared with an electrometer. The 

 tilted gold leaf electrometer of C. T. E. Wil- 

 son was used on account of its small capacity. 



The difference in the gold leaf deflection 

 due to twenty successive charges from the in- 

 side of the bottom of a copper beaker and to 

 the same number of charges from the inside 

 bottom of an exactly similar aluminium beaker 

 was 20.8 scale divisions, when the sensitivity 



of the instrument was 14 scale divisions for 

 an ordinary dry cell. 



A disc of tinfoil a little larger than the bot- 

 tom of the beaker was then pressed down inta 

 each beaker until it rested on the bottom and 

 was turned up about a centimeter around the 

 inside of the beaker. The zinc ball was then 

 charged as before by contact with the tinfoil 

 instead of the metal of the beaker. As a mean 

 of twenty such readings for each beaker made 

 exactly as before the electrometer deflection 

 amounted to 20 scale divisions for the differ- 

 ence of charge talten from the tin foil inside 

 the two beakers. This showed that the fixed 

 charges induced upon the zinc ball were due 

 almost wholly to the outside beakers instead 

 of the inside tinfoil. 



The beakers were then inverted and the tin- 

 foil discs were placed on the outside of their 

 bottoms and the zinc ball charged by contact 

 with the tinfoil as before. Here, where in- 

 ductive influence of the beakers was almost 

 wholly removed, the difference of the charges 

 taken from the tinfoil discs averaged only 1.2 

 scale divisions, which was not greater than 

 the probable error of the experiment. 



A third series of readings was then made 

 with the beakers loosely wrapped on the out- 

 side with tinfoil which was turned in for a 

 centimeter or so around the top. The zinc 

 ball was lowered into the beakers and charged 

 by contact with the bottom, as in the first 

 series of experiments, both with the tinfoil 

 around the beakers and with it removed. In 

 this series, the difference in deflection due to 

 the two beakers without the tinfoil was 23.4 

 scale divisions, while with the beakers wrapped 

 in tinfoil it was only 7.5 scale divisions. In 

 this case, since the bound charges induced by 

 the tinfoil wrapping upon the two beakers 

 were different from their normal fixed charges, 

 the charges which they, in turn, induced upon 

 the zinc ball were also different from the 

 charges which they induced with the tinfoil 

 wrapping removed. 



Summary 

 I have tried to show in the preceding paper 

 that metals, and probably all other bodies. 



