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Mr. W. Morris Jones : Frictional 



Fig. 4 shows the curves for some of the metals. In shape 

 they are, as might be expected, very similar to those of the 

 insulators. The maximum charge is, however, greater on 

 some o£ the metals than on any o£ the insulators. 



Fig. 4. 



With the metals, capacity plays an important part in the 

 value of the maximum charge generated. Three tin disks 

 1*2 cm. in diameter were mounted, one on ebonite and the 

 other two on brass cylinders 3 mm. and 1 cm. thick. On 

 being rubbed, the specimen mounted on the longer metal 

 cylinder gave the greatest maximum charge, and the disk on 

 ebonite gave the least, while the specimen on the short metal 

 cylinder gave a charge of intermediate value. The three 

 results in this case are shown in fig. 4. Apparently, there- 

 fore, the charge generated on a metallic specimen by a 

 given amount of work increases with the capacity of the 

 specimen. 



The following classification of the metals according to the 

 sign of the charge, shows that the metals examined can be 

 divided into three groups :— 



