1846] WRITINGS OF JOSEPH HENRY. 253 



It may be mentioned as an interesting fact, derived from 

 two independent sources of information, that large numbers 

 of small birds have been seen suspended by the claws from 

 the wire of the telegraph. They had, in all probability, been 

 instantaneously killed, either by a direct discharge, or an 

 induced current from a distant cloud while they were rest- 

 ing on the wire. 



Though accidents to the operators, from the direct dis- 

 charge, may be prevented by the method before mentioned, 

 yet the effect on the machine cannot be entirely obviated; 

 the residual current which escapes the discharge along the 

 perpendicular wires must neutralize, for a moment, the cur- 

 rent of the battery, and produce irregularity of action in the 

 apparatus. 



The direct discharge from the cloud on the wire is, com- 

 paratively, not a frequent occurrence, while the dynamic 

 inductive influence must be a source of constant disturbance 

 during the seasons of thunder storms; and no other method 

 presents itself to my mind at this time for obviating the 

 effect, but that of increasing the size of the battery, and 

 diminishing the sensibility of the magnet so that at least 

 the smaller induced currents may not be felt by the machine. 

 It must be recollected that the inductive influence takes 

 place at a distance through all bodies, conductors and non- 

 conductors; and hence no coating that can be put upon the 

 wire will prevent the formation of induced currents. 



I think it not improbable, since the earth has been made 

 to act the part of the return conductor, that some means will 

 be discovered for insulating the single wire beneath the sur- 

 face of the earth ; the difficulty in effecting this is by no 

 means as great as that of insulating two wires, and prevent- 

 ing the current striking across from one to the other. A 

 wire buried in the earth would be protected in most cases 

 from the effect of a direct discharge; but the inductive in- 

 fluence would still be exerted, though perhaps in a less 

 degree. 



The wires of the telegraph are too small and too few in 

 number to affect, as some have supposed, the electrical con- 



