PROTECTION FROM LIGHTNING. 



43 



However great* the peril may be such clouds have been traversed 

 without disastrous results. From many instances on record, I 

 select the following- : 



In August, 1150, an ascent was made of the little mountain 

 Boyer in France. Three-fourths the way up the mountain was a 

 stationary cloud, from which thunder was from time to time heard. 

 From the moment the cloud was entered, "the thunder no longer 

 manifested itself by sudden claps, alternating with intervals of 

 silence ; it now made a continual rumbling, resembling that of a 

 heap of walnuts rolled upon the floor. When the observer had 

 attained the summit of the mountain he found himself above the 

 cloud which had not ceased to be a thunder cloud, for it was 

 traversed by brilliant lightnings, and loud detonations issued from 

 it." 



Observers upon the Pyrenees in the midst of thunder clouds 

 have noticed that their hair and the tassels of their caps stood on 

 end, and that a hissing sound was produced from prominent points. 

 A position above a thunder cloud cannot be regarded as un- 

 questionably safe. Lightning has been known to issue from the 

 upper surfaces of clouds, and strike objects upon the summit of 

 mountains above them. Thus on May 1st, 1100, seven persons 

 were killed in a church on the summit of Mount St. Ursula in 

 Styria. 



The thunder which ordinarily accompanies a discharge of light- 

 ning, is regarded as resulting from the collision of particles of the 

 atmosphere as they reenter the partial or total vacuum produced 

 by the lightning in its swift passage through the air. As is well 

 understood the interval between the flash and the report in- 

 dicates approximately the distance of the cloud, or rather of that 

 part of the cloud from which the sound which first reaches the 

 ear, emanates, an allowance of about five seconds for the distance 

 of a mile being required. The largest interval mentioned by any 

 observer is 12 seconds, indicating a distance of nearly 15 miles. 

 The next longest interval recorded is 50 seconds, corresponding 

 to a distance of about ten miles. It seems remarkable that the 

 sound of thunder has not more of a diffusive character. The 

 sound of cannon may be heard to a much greater distance. 



The average interval between flash and report is 12 seconds, 

 and the shortest interval noted less than one-half a second. The 

 average duration of peals of thunder is 22 seconds, and the long- 

 est duration on record is 56 seconds. The prolonged sound in 



