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On another occasion, a continued stream of electricity was observed 

 to pass between two points at a break in the wire, presenting the ap- 

 pearance of a gas-hght ahuost extinguished. A constant effect of this 

 kind indicates a constant accession of electricity at one part of the 

 wire, and a constant discharge at the other. 



3. The natural electricity of the wire of the telegraph is liable to 

 be disturbed by the ordinary electrical induction of a distant cloud. 

 Suppose a thunder-cloud, driven by the wind in such a direction as 

 to cross one end of the line of the telegraph at the elevation, say of a 

 mile; during the whole time of the approach of the cloud to the point 

 of its path directly above the wire, the repulsion of the redundant elec- 

 tricity with which it is charged would constantly drive more and 

 more of the natural electricity of the wire to the farther end of the 

 line, and would thus give rise to a current. When the cloud arrived 

 at the point nearest to the wire, the current would cease for a mo- 

 ment; and as the repulsion gradually diminished by the receding of 

 the cloud, the natural electricity of the wire would gradually return 

 to its normal state, giving rise to a current in an opposite direction. 

 If the cloud were driven by the wind parallel to the line of the tele- 

 graph, a current would be produced towards each end of the wire, 

 and these would constantly vary in intensity with the different posi- 

 tions of the cloud. Although currents produced in this way may be 

 too feeble to set in motion the marking apparatus, yet they may have 

 sufficient power to influence the action of the current of the battery 

 so as to interfere with the perfect operation of the machine. 



4. Powerful electrical currents are produced in the wires of the 

 telegraph by every flash of lightning which takes place within many 

 miles of the line, by the action of dynamic induction ; which differs 

 from the action last described, in being the result of the influence of 

 electricity in motion on the natural electricity of the conductor. The 

 effect of this induction, which is the most fruitful source of disturb- 

 ance, will be best illustrated by an account of some experiments of 

 my own, presented to the Society in 1843. A copper wire was sus- 

 pended by silk strings around the ceiling of an upper room, so as to 

 form a parallelogram of about sixty feet by thirty on the sides; and 

 in the cellar of the same building, immediately below, another paral- 

 lelogram of the same dimensions was placed. When a spark from 

 an electrical machine was transmitted through the upper parallelo- 

 gram, an induced current was developed in the lower one, sufficiently 

 powerful to magnetize needles, although two floors intervened, and 

 the conductors were separated to the distance of thirty feet. In this 



