Popular Science Monthly 



367 



are visible far out at sea. Dr. Knoche once 

 saw them from a distance of three hundred 

 miles. Something akin to "Andes light- 

 ning" has occasional- 

 ly been reported from 

 other mountainous 

 regions of the world. 

 "Ball" lightning 

 takes the form of a 

 fiery mass (not al- 

 ways globular) , which 

 generally moves 

 quite deliberately 

 through the air or 

 along the ground, 

 and in many cases 

 disappears with a 

 violent detonation. 

 Many ingenious ex- 

 planations of this 

 strange phenomenon 

 have been offered, 

 but none of them is 

 wholly satisfactory. 

 An immense amount 

 of statistical and de- 

 scriptive information 

 concerning ball light- 

 ning has been gath- 

 ered in recent years; 

 notably by Dr. 

 Ignazio Galli, in 

 Italy. 



Do Lightning-Rods 

 Help? 



Turning, now, to 

 the subject of light- 

 ning-rods, it may be 

 stated emphatically 



that the reputation of these devices has 

 been fully rehabilitated in this country. 

 The Weather Bureau has always strongly 

 advocated their use, 

 and Prof. J. Warren 

 Smith, of that Bu- 

 reau, has recently as- 

 sembled some im- 

 pressive statistics in 

 their favor, compiled 

 from the records of 

 fire insurance com- 

 panies. 



Damage by light- 

 ning is comparative- 

 ly rare in towns, 

 where metal roofs, 

 steel frames of build- 

 ings, tall chimneys 

 and other objects 

 constitute an assem- 

 blage of conductors 

 capable of dissipat- 

 ing the electrical 

 charge ofl passing 

 clouds without ' dis- 

 ruptive discharges 

 between the clouds 

 and the earth. On 

 the other hand, light- 

 ning is a thing to be 

 reckoned with in the 

 rural districts. It is 

 estimated that the 

 total property loss 

 from this cause aver- 



A discharge of lightning of some duration, 

 which is photographed as a broad ribbon of fire 



The correct location and distribution of 

 lightning rods on various kinds of buildings 



ages $>», 000,000 a 

 year in this country; 

 also that about 1,500 

 persons are struck by 

 lightning in the same period. Nine- 

 tenths of these accidents occur in rural 

 localities. 



At present, according to an estimate 

 of the Bureau of Standards, not more 

 than fifteen to twenty per cent of the 

 buildings in the United States which 

 are liable to damage by lightning are 

 protected in any manner against it. Yet, 

 to quote from the same authority, "such 

 evidence as is available on the effectiveness 

 of lightning-rods indicates that, taking 

 rods as they come in the general run of 

 installations, they reduce the fire hazard 

 from lightning by eighty to ninety per cent 

 in the case of houses, and by as much as 

 ninety-nine per cent in the case of barns." 

 In Technologic Paper No 56 the whole 

 question of protection against lightning is 



