WARMING THE AIR 127 



Atmospheric electricity is not different from the electricity 

 which is produced by friction. Benjamin Franklin showed 

 this by his famous kite experiment in 1752. Since about 

 75,000 volts are necessary to produce a spark one inch long, 

 it can be calculated that a flash of lightning over a mile long 

 represents a voltage which cannot be comprehended. 



References : 



1. 1103:175-179. Atmospheric Electricity. 



2. 1304:267-268. Thunderstorms. 



3. 1803 : 249-250. Lightning and Lightning Rods. 



4. Farmer's Bulletin No. 367. Lightning and Lightning Con- 



ductors. 



a. 1102:265-271. Atmospheric Electricity. 



b. 1207 : 164-167. Atmospheric Electricity. 



c. 1302 : 325-326. Thunderstorms. 



d. 1303 : 65-66. Thunderstorms. 



e. 1305 : 106-108. Atmospheric Electricity. 

 /. 1309 : 275-278. Atmospheric Electricity. 



g, 1312 : 395-397. Electrical Phenomena in the Atmosphere. 



~\ h. 1801 : 334-336. Atmospheric Electricity. 



i. 1804:460-461. Atmospheric Electricity. 



j. 1805 : 368. Lightning and Lightning Rods. 



k. 1808 : 287-290. Atmospheric Electricity. 



93. WARMING THE Am 



Since the earth has become cold on the surface, we must 

 remember that all the heat which we enjoy comes from the 

 sun. Air is heated in two ways, one directly, the other in- 

 directly; the greater amount of heat is obtained by the in- 

 direct method. We remember that if a substance is trans- 

 parent, the energy of the sun passes through easily, and 

 therefore will not warm the material through which it passes. 

 Since the air is very transparent, the energy of the sun passes 



