50 



Proceedings of the Royal Irish Academy. 



the rise was slower than in the case when the metal charged negatively, and 

 the maximum occurred at a higher pressure. The pressure corresponding to 

 maximum charging was also different for the two metals, being about - S mm. 

 for copper and 1*25 mm. for iron. From all these results it would appear that 

 the pressure at which maximum production occurs is determined by the 

 substance which is charging positively ; thus different metals taking a nega- 

 tive charge gave the same point of maximum production when the same 

 rubber w.is used, but a different point with another rubber. Again, copper 

 and iron gave a maximum at different pressures when taking a positive 

 charge. 



In all tl experiments at low pi the air was well dried with 



phosphorus i"'m i the effects of drying previously recorded must be 



borne in mind in interpreting the present results. The rubber no doubt 

 insulates well when well dried and theref"i>- retains the charge of opposite 

 to that on the id if for any reason the n bbei losl ite charge 



more Freely at a ['articular pressure, the form of the cm ves might be explained. 

 B we do not think that a sufficient explanation ound along those 



lines, and it w inld therefore appear that the actual rate of production of 

 ch irg b the residual pressure of the gas as shown on the curves. 



This press - under further examination in the laboratory. 



\\v pose at this stage to discuss the theory of the results 



contained in this paper. Indeed, the main object in publishing the results 

 in their prw m is to show that it is quite possibb- to make measure- 



ments on frictional electricity with such a degree of accuracy and consistency 

 •omplete study of the subject. 



