Charmng fhroiioli Ion Absorption . 597 



of the difference in the mobility of the ions. We can also 

 no lontvoracce])tthe theory that in all places protected against 

 the formation of an electrical field, snch as within conductors, 

 then» is a continual stream of neoative ions out of the air, 

 for tho positive ions which this would leave behind are all 

 within molecular distanees of the surface, so hold an equal 

 cjuantity of negative electricity as a " bound charge,'' no 

 electricity being al)le therefore to appear as a free charge. 



80 far we have considered air at rest, we must now ask 

 what will be the effect of setting the air in motion. At iirst 

 sight it would appear that as fresh air is always moving past 

 the conductor more negative than positive ions would reach 

 the surface, and as a surfiice layer of positive ions would be 

 unable to form, a negative charging could be expected. But 

 when we consider conductors in air as being electrodes in 

 an electrolvte it is difficult to see how motion could affect 

 the potential which they had taken up when the air was at 

 rest. In order to put this question to the test of experiment, 

 air was driven past insulated metals within the cage described 

 above, by means of a fan attached to an electric motor. 

 Although the wind so produced had a velocity greater than six 

 metres a second no change could be observed in the charge 

 which the metal had attained before the fan was set in motion. 

 Thus when a piece of the same netting as that of which the 

 cao-e was made was hung w^ithin the cage, the needle of the 

 electrometer connected to it remained at zero with or with- 

 out the fan in motion. When copper w^as used as the 

 insulated metal it took a positive charge as described above, 

 and this charge was the same whether the fan was in motion 

 or not. The electrical state of the fan itself was then 

 investio-ated by carefully insulating it from the axis of the 

 motor, but no charging, except a very uncertain positive one, 

 could be observed, although the fan, which was 50 cms. in 

 diameter, produced a wind with the velocity stated above. 

 It must be stated that an uncertain positive charge appeared 

 also sometimes on the metals which were subjected to the 

 w^nd, but as it never produced more than a tenth of a volt 

 potential, and could not Ije obtained at will, no conclusion 

 can be drawn from it. The result of this experiment favours 

 the second method described above of considering what will 

 happen when air is in motion, but does not disprove the 

 former, all that can be said for certain is that a conductor 

 has not yet been charged as a result of its motion relative to 

 the naturalbi ionized air of the laboratory. 



Although it has been impossible to charge a conductor by 

 this method, yet a very great absorption of ions takes place 



Phil. Mag. S. 6 Vol. 6. No, 35. Nor. 1903. 2 R 



