-1859] WRITINGS OF JOSEPH HENRY. 383 



the current will cease for a moment, and as the repulsion 

 gradually diminishes by the receding of the cloud the natu- 

 ral electricity of the wire will return to its normal condition 

 by a current opposite to that which was first manifested. 

 Since the thunder clouds over the greater portion of the 

 United States move from west to east, lines in a north and 

 south direction are more liable to currents of this class, which 

 may be denominated those of statical induction. 



There is another class of currents which although they 

 continue but for an instant are more intense than the pre- 

 ceding, giving rise to vivid sparks, and are due to the dynamic 

 induction at a distance of a discharge from a cloud to a cloud, 

 or from a cloud obliquely to the earth. 



The greatest intensity is produced when the path of the 

 lightning is parallel to the line of the telegraph, and in this 

 case, under favorable circumstances, sparks and shocks may 

 result from a discharge between two clouds at the distance 

 of several miles. In these inductive actions there is no trans- 

 fer of the electricity from the cloud to the wire, but simply 

 the disturbance of the natural electricity of the conductor 

 by the repulsive energy exerted at a distance. As already 

 stated, nothing screens this induction ; for like magnetism 

 and gravitation, it acts as freely through the roof of a house, 

 the air, and all other non-conducting materials as it probably 

 would do through void space. A similar result is produced 

 on long lines of railway, and sparks have been observed 

 at the joining of the rails not in perfect metallic connection, 

 particularly at the turn-tables. 



The electrical telegraph is sometimes disturbed by other 

 influences. It is evident from what we have said in reference 

 to elevated bodies, that if a line of wire extends over a high 

 hill the intensity of electricity will be greater at the high 

 points than below, particularly during the occurrence of fogs ; 

 the wire will tend to absorb the electricity of the air, and 

 transmit it from the higher to the lower portions; also dur- 

 ing the fall of rain and snow on one portion of a long wire 

 while clear weather exists at another, there would be a cur- 

 rent of electricity observed in the intermediate portion. 



