ELECTRICITY. 347 



a very evident electric spark. Others succeeded, 

 even before the string was wet, so as to put the 

 matter past all dispute; and when the rain had 

 wetted the string, he collected the electricity very 

 copiously. This happened in June, 1752. 



The same experiment has been often successfully 

 repeated: but it is not unaccompanied with dan- 

 ger; since frequently such a quantity of electric 

 matter is suddenly brought down, that several 

 persons have been hurt by it, and a professor at 

 St. Petersburg was killed in this manner. 



A grand practical application of this discovery 

 has been, to secure buildings from being damaged 

 by lightning. 



This great end is accomplished by the cheap, 

 and seemingly trifling apparatus, of a pointed me- 

 tallic rod, fixed higher than any part of the 

 building, and communicating with the ground, or, 

 rather, the nearest water. This rod the liffhtnina: 

 is sure to seize upon, preferably to any other part 

 of the building, unless it be very large and ex- 

 tended; in which case, rods may be erected at 

 each extremity; by which means this dangerous 

 power is safely conducted to the earth, and dissi- 

 pated without doing any harm to the edifice. 



Lofty trees are often struck by lightning; and 

 in a thunder storm it is not safe to seek for shelter 

 under them. In this case the safest place is in the 

 open field. Persons carrying arms or tools have been 

 often killed by lightning, which has been attracted 

 by the metallic substances. When a house is 

 struck, it may be observed that it is by the metallic 

 parts that the lightning makes its way to the earth; 

 frequently by the bell wires which it often melts, 

 and when there is an interruption in the continuity 

 of the conducting substance, it darts to the nearest 



