Feb., 1915.] 
Efficacy of Lightning Rods. 
439 
materially in the quiet interchange of electricity that is constantly 
talcing 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 information 
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 
information obtainable indicates that 31% cf 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 actually 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%. 
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 
