202 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



that a storm is in the neighborhood. Usually, however, the first 

 warning must come from employees distributed over the system, who, 

 as part of their regular duties, report to the load dispatcher the 

 location, direction of travel, and severity of storms near the system. 

 The dispatcher can determine whether it is liable to affect his system, 

 and can then make the necessary changes in system set-up to minimize 

 the effect of the storm. 



AMMUNITION STORAGE 



Lightning is a real hazard to ammunition storage depots. Where a 

 choice of locations is possible, a study of thunderstorm conditions 

 should be of value in selecting a location offering minimum exposure. 

 Alexander's charts of thunderstorm frequency should be of value in 

 determining the general region. The most favorable location in this 

 region can then be determined by a localized study of topographical 

 and meteorological factors, advantage being taken of knowledge 

 of the type of storm most prevalent, the location of topograpliical 

 features such as combinations of mountains and moisture sources 

 which are known to serve as thunderstorm "breeders," prevailing 

 wind directions, preferred stonn paths, etc. At times such depots 

 may be located in a position taldng advantage of topographical 

 features offering natural shielding against direct strokes. 



OIL STORAGE 



Wlicre a choice of location for the storage of oil is possible, a study 

 of thunderstorm conditions similar to that described for ammunition 

 depots should be worth-while. Here, again, comparatively minor 

 cliangcs in storage location may result in a considerable decrease in 

 lightning exposure. 



Although exposure to hghtning may be reduced by proper location, 

 this reduction should not be construed to justify a reduction or elimi- 

 nation of lightning protective equipment where hghtning is particu- 

 larly hazardous to the material to be protected. For example, while 

 Alexander's charts show that California enjoys comparative freedom 

 from thunderstorms, still occasional severe storms do occur there 

 and the elimination of protective equipment would be unwise. In 

 1926, miUions of dollars worth of oil and equipment in that State 

 were destroyed by fires set by lightning. 



RfiSUMfi 



In the foregoing, Simpson's, Elster and Geitcl's, and Wilson's the- 

 ories of the electrification of thunderclouds are reviewed. Experimen- 

 tal evidence and observations bearing upon these theories are given 

 consideration and the characteristics of actual thunderstorms are de- 

 scribed. Five types of thunderstorm formation — heat, mountain. 



