-1859] WRITINGS OF JOSEPH HEXRY. 389 



have shown that but a comparatively small amount of de- 

 velopment of electricity is sufficient to produce great mechan- 

 ical effects. Faraday has even asserted that the quantity of 

 electricity necessary to de-compose a single grain of water, 

 (and consequently the electricity which would be evolvod by 

 the re-composition of the same elements) would be sufficient 

 to charge a thunder cloud, provided the fluid existed in the 

 free state in which it is found at the surface of charsfed con- 

 ductors. A similar inference may be drawn from the great 

 amount of electricity developed by the friction of the small 

 quantity of water existing in steam, as the latter issues 

 through an orifice connected with the side of the boiler. We 

 also find that an iron rod of three-fourths of an inch in 

 diameter, is of sufficient size to transmit to the earth with- 

 out any danger to surrounding objects a discharge from the 

 clouds, which may be attended with a deafening explosion 

 and with a jar of thunder powerful enough to shake the 

 building to its foundation. 



The intrepid physicist, De Raumer, sent a kite up into 

 the air to the height of 400 or 500 feet, in the cord of which 

 was inserted a fine wire of metal. During a thunder-storm 

 he drew from the lower extremity of the cord not mere sparks 

 but discharges nine or ten feet long and an inch broad. 



Beccaria erected a lightning-rod which was separated in 

 the middle by an opening, the upper part being entirely 

 insulated. During thunder-storms intense discharges darted 

 incessantly through the opening. So constant were these 

 that neither the eye nor the ear could readily perceive the 

 intermission. 



" No physicist," says Arago, " will contradict me when I say 

 that each spark taken singly would have given a shock 

 attended with pain, that ten sparks would have numbed a 

 man's arm, and a hundred would have proved fatal. Now 

 a hundred sparks passed in less than ten seconds, and hence 

 in every ten seconds there was drawn from the cloud a 

 quantity of electrical energy sufficient to kill a man, and six 

 times as much in every minute." Arago calculates in this 

 way that all the lightning conductors of the building in 



