-1859] WRITINGS OP JOSEPH HENRY. 395 



tricity is constantly renewed; a fact sufficiently demon- 

 strated by the observation that a thunder storm, through its 

 whole course of several hundred miles in extent, continually 

 gives discharges to the earth. Notwithstanding the instances 

 given by Arago of the diminution of discharges of lightning 

 after the erection of the rod, the fact is established by obser- 

 vation, experiment, and theory, that the rod does attract the 

 lightning, and that it receives the discharge not alone 

 silently, but explosively. The points of the conductors are 

 frequently melted, and although in cases in which this 

 occurs, the discharge passes harmlessly to the earth, yet in 

 some instances the explosion might not have taken place 

 had the rod not been present. 



The following instructive illustration of the action of a 

 very elevated conductor in transmitting a discharge from a 

 thunder cloud is furnished us by Mr. Henry J. Rogers, tele- 

 graph engineer, who was himself an eye-witness of what he 

 relates : 



" In accordance with my promise I will endeavor to give 

 you a brief description of the effect produced by atmospheric 

 electricity at the House Telegraph mast, erected at the Pali- 

 sades on the west side of the Hudson river, in the vicinity 

 of Fort Lee, New Jersey'', and distant about ten miles from 

 the City Hall, New York, during a terrific thunder storm 

 which occurred on Friday, June 17, 1853, between three and 

 four o'clock p. M., while I was on an official visit. 



" Before I proceed with the description it will be necessary 

 to explain that the wires of the House and Morse telegrapli 

 lines cross the Hudson river between Fort Washington and 

 the Palisades, inasmuch as this is the narrowest part of the 

 river in the vicinity of New York, and the elevation of the 

 land at the Palisades renders it a desirable place for suspend- 

 ing the wires from one shore to the other, so as to allow 

 vessels of large size to pass under them free from interruption. 



" The mast to support the wire was 266 feet in length, 

 and was erected on the top of the columnar wall of the Pali- 

 sades, which at this place is 298 feet above the river, as de- 

 termined by trigonometrical measurement. The top of the 

 mast was therefore 564 feet above the water, and was suf- 

 ficiently elevated to allow for the unavoidable sagging of 

 the telegraph wire, and to leave sufficient distance for vessels 

 to pass beneath. 



