Current and on the Origin of Atmospheric Electricity. 365 



deduced. As thus carried out the method is the same in principle 

 as that hitherto adopted, the difference being in the measurement 

 of the dissipation factor, which, according to the method of this 

 paper, is obtained by observations on the current through a con- 

 ductor exposed under normal conditions in the free atmosphere. 

 There is the further advantage that if we use the same conductor 

 exposed at the same height and otherwise under similar con- 

 ditions in successive experiments, the charge on the conductor 

 will be proportional to the potential gradient ; and when once the 

 appropriate reduction factor has been obtained, the potential 

 gradient is measured concurrently with the other measurements, 

 and without the disturbing influences of any of the various forms 

 of collectors. 



To make the method of measuring earth-air currents which is 

 here suggested practicable, a portable electrometer, suitable for 

 measurements in the neighbourhood of zero potential and provided 

 with a compensator for maintaining the potential at zero, is re- 

 quired. Such an electrometer was described and its application 

 to the present purpose suggested in the paper already mentioned. 

 The main object of the present paper is to indicate how the 

 method has worked in practice. 



The figure (Fig. 1) shows the apparatus which was attached 



Fig. 1. 



for the purpose of the present measurements to the electrometer 

 already described. Supported on a vertical rod screwed into the 



