Current and on the Origin of Atmospheric Electricity. 377 



potential, measured exactly as before. For the measurements 

 of charges being all made in terms of the compensator readings, 

 they are independent of the capacity of the rest of the system. 

 The test-plate may for example be covered with turf and the 

 dissipation factor determined for this. Measurements of this kind 

 were made on the hill-top on April 17th, observations with and 

 without the turf being taken alternately. The test-plate was 

 about 60 cms. above the ground. 



With turf 

 Without turf 

 With turf 

 Without turf 



Time 



3.44 

 3.50 

 3.56 

 4.3 



Charge 



Leak 

 per minute 



11-8 

 3-7 



15-3 

 4-4 



1-05 

 •33 



1-35 

 •35 



Dissipation 

 factor 



8-9 

 8-9 

 8-9 

 7-9 



The charge with the turf on was considerably greater than 

 without it, owing to the fact that it projected considerably above 

 the level of the guard plate ; the current was however increased in 

 approximately the same ratio, so that the dissipation factor is not 

 sensibly altered. 



I have also made measurements by the same method of the 

 charge upon and current through a growing plant exposed 

 to the earth's field and kept at zero potential. To make a 

 measurement of this kind the plant growing in a flower-pot is 

 placed on the test-plate, and a metal cover large enough to admit 

 of being removed and replaced without danger of contact with the 

 plant was put over it, resting on the guard plate. The measure- 

 ments were then made as before. The plant which I used to test 

 this application of the method to such measurements was a young 

 wall-flower, 14 cms. high and 8 cms. across at the widest part, the 

 whole height with the pot being about 20 cms. ; the cover was 

 cylindrical, 22 cms. high and 12"5 cms. in diameter. The measure- 

 ments were made in a garden, in which the electric field was very 

 much weakened by the shielding action of buildings, trees and 

 telegraph wires. The charge on the plant was about 20 times that 

 on the test-plate, as found on making alternate exposures with and 

 without the plant on the test-plate, reaching even in the weak 

 electric field of the garden to as much as one electrostatic unit. 

 The observations did not show any evidence that the dissipation 

 factor was different for the plant and test-plate, but a large series 

 of comparisons would be required to test to what extent, if at 

 all, it differs. The experiments tried however were sufficient 

 to prove the practicability of the method. 



