-1859] WHITINGS OF JOSEPH HENRY. 341 



made by the author, which consisted in placing one end 

 of a copper wire (a tenth of an inch in diameter) beneath 

 the water of a well, its upper end being terminated by a 

 small ball, and throwing on it sparks of electricity from a 

 globe of a foot in diameter. Although in this case the con- 

 ductor was as perfect as possible, yet sparks sufficiently in- 

 tense to explode the oxy-hydrogen pistol were obtained from 

 the wire throughout its whole length. 



This effect was not due, as some have supposed, to the 

 tendency of the electricity to seek another passage to the 

 earth, as may be shown by catching the spark in a Leyden 

 jar ; but it was solely the effect of a transient charge of elec- 

 tricity passing along the surface of a conductor from one 

 extremity to the other. 



The phenomena may be expressed generally by the state- 

 ment that when electricity is thrown explosively as it were, 

 on the end of an insulated conductor, by a disruptive dis- 

 charge through the air, it does not pass silently to the 

 earth, but tends in part to be given off in sparks to all 

 surrounding bodies. It is on this account that we object to 

 the otherwise admirable arrangement of Sir W. Snow Harris 

 for the protection of ships from lightning. Though the 

 main portion of the discharge of electricity is transmitted 

 innoxiously to the ocean by means of the slips of copper 

 which are carried down along the mast and through the 

 bottom of the vessel to the sheathing beneath, as proposed 

 by him, yet we consider it safer to conduct it across the deck 

 and over the sides of the vessel to the copper sheathing. It 

 is true, the quantity which tends to fly off laterally from 

 the rod is small, yet we have shown by direct experi- 

 ment that it is sufficient even when produced by the elec- 

 tricity of a small machine, to set fire to combustible materi- 

 als ; and therefore it cannot be entirely free from danger in 

 a ship, loaded for example with cotton. 



The atoms of electricity, in their transfer from one body 

 to another, still retain their repulsive energy ; and if the 

 discharge be not very large in proportion to the size of the 

 conductor, it will be principally transmitted at the surface. 



