Feb., 1915.] Efficacy of Lightning Rods. 439 



materially in the quiet interchange of electricit}^ that is constantly 

 taking place between the atmosphere and the earth, and that the 

 rods should lead a disruptive discharge safely to the earth. 



As a result, lightning rods are being put up, especially on bams 

 in the country districts and Mutual Fire Insurance Companies 

 are raising the question as to their efficacy. 



To aid in answering this question the writer was directed 

 by the Chief of the U. S. Weather Bureau to collect infoiTiiation 

 for the Annual Meeting of the National Association of Mutual 

 Fire Insurance Companies held in Columbus, in September, 1914. 



Letters were therefore sent out to Mutual Companies in nearly 

 every state in the Union, particularly those in rural districts. A 

 large number of replies have been received and these have been 

 summarized in the attached table. 



This table shows that in 1912 and 1913 about 200 mutual 

 companies doing a business of fully $300,000,000, had 1,845 

 buildings struck by lightning. And of the number struck by 

 lightning, 67 only were equipped with lightning rods. 



Do Lightning Rods Prevent Lightning Strokes? — The best 

 infomiation obtainable indicates that 31% of the buildings 

 insured by these companies were equipped with lightning rods. 

 This being the case, the expectation would be that of the 1,845 

 struck by lightning, 31% or 572 would be rodded, but in fact 

 only 67 had rods of any kind. The number struck is therefore 

 only 10% of the expected number, and the efficiency of the light- 

 ning rod in actuallv preventing lightning strokes is shown to be 

 90%. 



In a report covering the past 5 years, 51 different companies 

 having nearly 95,000 buildings insured, had 660 buildings struck 

 by lightning and only 21 of these had lightning rods. Fully 

 34% of their buildings are rodded, so the expectation would be 

 that 34% of 660, or 224 would be rodded. In fact only 21, or 9% 

 were rodded, showing that out of every 100 buildings struck by 

 lightning, 91 of them were without lightning rods and only 9 had 

 rods. 



A table made up from 67 different companies in Missouri, 

 Illinois and Ohio, showed practically the same efficacy. Five 

 companies doing business in Illinois, Missouri, and Nebraska 

 with over 18,000 buildings insured, with reports covering a 

 longer period of years, the shortest being 13 years and the longest 

 25 years, never have had a building burned or even materially 

 damaged by lightning that was equipped with a lightning rod. 

 And they report over 50% of their buildings rodded. This is 

 efficiency of 100%o- 



If we should omit the few companies who have had damage 

 on rodded buildings, we would still have reports from over 100 

 Farm Mutual Insurance Companies with over 400,000 buildings. 



