]70 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1925 



When lightning strikes an object great damage is generally done. 

 However, it is not necessary for lightning to actually strike an object 

 to cause damage. A discliargo to earth inay cause sparks in distant 

 oil tanks or powder mazagines or destructive voltages on transmis- 

 sion lines. Voltages that occur by this "wireless" action are said to 

 be induced. 



LIGHTNING RESEARCH 



A study of lightning is of scientific importance because there is 

 manifest in the (lash the dynamic etlect of the electrons and ions, 

 the elemental bricks of which it is believed that all matter is made; 

 it is of engineering importance because an exact knowledge of the 

 characteristics of lightning will make it jDOssible to protect life, 

 buildings, powder magazines, od tanks, and transmission lines against 

 it. The ideal method of making such a study is by observations of 

 natural lightning in the field and researches with artificial lightning 

 in the laboratory. Such a combined study was made in the laboratory 

 and in the mountains of Colorado. 



TWO MILLION-VOLT LIGHTNING GENERATOR 



The artificial lightning was produced by a lightning generator 

 which supplies 2,000,000 volts above ground, higher than most volt- 

 ages induced on transmission lines. (See fig. 7.) The discharge 

 from the lightning generator produces a loud, sharp explosive re- 

 port, and the power is of the ordei" of millions of kilowatts for a 

 few millionths of a second. Currents as high as 10,000 amperes 

 have been obtained. The voltages increase at the rate of millions 

 of volts per second. In common with natural lightning, artificial 

 lightning has interesting characteristics. 



The large, wooden posts shown in Figure 8 were split by a 

 1,500,000- volt discharge. Longitudinally through the center of the 

 stick is a hole of less tlian one thirty-secondth inch (0.8 mm.) in 

 diameter. The wood around this hole has a " fuzzy " appearance, 

 but does not appear burned. Immediately after being blown apart 

 the wood has an odor of the gases of destructive distilhition. Ap- 

 parently these gases are formed suddenly by the discharge, and pro- 

 duce such high pressures that the wood is blown apart with great 

 violence. 



Even metal may be " punctured," as shown in Figure 9. In this 

 case the metal formed a coating on a glass plate. The lightning 

 discharge punctured the j)late to the metal. The holes were appar- 

 ently caused by the sudden formation of gases between the metal 

 and the glass. A discharge striking through water disrupts it in 

 much the same manner as oil is disrupted at 60-cycle voltages. 



