180 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1925 



enerfry 13,500 kilowatt-seconds or 3.8 kilowatt-hours. This enerj^y 

 is sufficient to operate an automobile about 5 miles or an electric 

 toaster for a day. Since this ener<!;y is dissipated in a very short 

 time, the power may be several thousand million kilowatts or horse- 

 power. The effect is thus explosive and destructive. 



The discharge of the cloud is probably generally nonoscillatory 

 and takes place in the manner shown in Figure 15. A convenient 

 measure of time is the microsecond or millionth of a second. The 



^.g Time in Micro Seconds 



Fig. 15. — Transleutss for " cloud " discharge to eaitli 



time of discharge may be ver}' much longer if the resistance of the 

 path is higher. 



It may be of interest to point out that the voltage of the light- 

 ning generator is about 2 per cent and the power about 0.02 per 

 cent of natural lightning. This practically corresponds to the light- 

 ning energy that appears on transmission lines. 



LIGHTNING ON TRANSMISSION LINES 



Most lightning disturbances on transmission lines occur by elec- 

 trostatic induction and not by direct stroke. A charged cloud causes 

 an electrostatic lield to earth. Part of the field will terminate on 



