252 WRITINGS OP JOSEPH HENRY. [1846 



The pungency of the spark was also, as might have been 

 expected, very great. When a small break was made in the 

 circuit, and the parts joined by the forefinger and thumb 

 the discharge transmitted through the hand affected the 

 whole arm up to the shoulder. I was informed by the 

 superintendent that on another occasion a spark passed over 

 the surface of the spool of wire surrounding the legs of the 

 horse-shoe magnet at right angles to the spires ; and such 

 was its intensity and quantity that all the wires across which 

 it passed were melted at points in the same straight line as 

 if they had been cut in two by a sharp knife. 



The effects of the powerful discharges from the clouds may 

 be prevented, in a great degree, by erecting at intervals along 

 the line, and aside of the supporting poles, a metallic wire 

 connected with the earth at the lower end, and terminating 

 above at the distance of about half an inch from the wire of 

 the telegraph. By this arrangement the insulation of the 

 conductor will not be interfered with, while the greater 

 portion of the charge will be drawn off. I think this pre- 

 caution of great importance at places where the line crosses 

 a river, and is supported on high poles. Also in the vicinity 

 of the office of the telegraph where a discharge, falling on 

 the wire near the station, might send a current into the 

 house of sufficient quantity to produce serious accidents. 

 The fate of Professor Richman, of St. Petersburg, should be 

 recollected, who was killed by a flash from a small wire, 

 which entered his house from an elevated pole, while he was 

 experimenting on atmospheric electricity. 



The danger however which has been apprehended from 

 the electricity leaving the wire and discharging itself into a 

 person on the road is, I think, very small; electricity, of 

 sufficient intensity to strike a person at the distance of eight 

 or ten feet from the wire, would, in preference, be conducted 

 down the nearest pole. It will however in all cases be most 

 prudent to keep at a proper distance from the wire during 

 the existence of a thunder storm in the neighborhood. 



