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MR. C. T. R. WILSON: INVESTIGATIONS ON LIGHTNING DISCHARGES 
were recorded ; on the remaining day, however (June 16) about twice as many 
negative as positive discharges were recorded (74 negative, 38 positive). It is 
perhaps natural to associate the excess of positive over negative discharges with the 
excess of positive electricity found by Simpson* and others to be carried down in 
rain, the greater part of the charge transferred from the atmosphere to the earth by 
the rain of the thunderstorm being perhaps returned in lightning discharges. (See 
however Sections XIX. and XX.) 
IV. Magnitude 'of the Changes Produced in the Electric Field by Lightning 
Discharges at Different Distances. 
The approximate distance of each lightning flash which caused a disturbance on 
the photographic trace was, when possible, determined by observing the time interval 
between the discharge and the thunder associated with it. The beginning of each 
