176 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fJVNK, 



ON THE INDUCTION OF ATMOSPHERIC ELECTRICITY ON 



THE WIRES OF THE ELECTRIC TELEGRAPH. 



By Professor Joskph Henry. 



The action of llie electricity of the atmosphere on the wires of the 

 electrical telegraph is at the present time a suhject of much iin|)urt- 

 ance, both on account of its practical hearing, anil the numher of 

 purely scientific questions which it involves I have accordingly 

 given due attention to the letter referred to me, and have succeed- 

 ed in collecting a nuinher of facts in reference to the action in 

 question. Some of these are from the observations of different per- 

 sons along the principal lines, and others from niv own investiga- 

 tions during a thunder-storm on the lOtli of Juni-, when I was so fortu- 

 nate as to be present in the office of the tehgraph iii Philadelpliia, 

 while a series of very interesting electric. d ph^'nomena was exhibited. 

 In connexion with the facts derived from these sources, I niust ask 

 the indulgence of the Society in frequently referring, in the course of 

 this cotniiHuiication, to the results of my previous investigations in 

 dynamic electricity, accounts of which are to be found in the Proceed- 

 ings and Transactions of this Institution.* 



From all the information on the subject of the action of the electri- 

 city of the atmosphere on the wires ol the telegraph, it is evident that 

 ert'ects are produced in several different nays. 



1. The wires of the telegraph are liable to be struck by a direct 

 discharge of lightning from the clouds, and several cases of this kind 

 have been noticed during the present season. About the £Olh of 

 May the lightning struck the elev.ited part of the wiie, which is sup- 

 ported on a high mast at the place where the telegraph crosses the 

 Hackensack River. The fluid passed along the wire each wav, from 

 the point which received the discharge, for several miles, striking off 

 at irregular intervals down the supporting poles. At each place 

 where the discharge to a pole took [ilace, a number of sharp explo- 

 sions were heard in sucdssion, resembling the rapid reports of several 

 rifles. During anollier storm, the wire was struck in two places in 

 Pennsylvania, on the route between Philadelphia and New York; at 

 one of these places twelve poles were struck, and at the otlicr eight. 

 In the latter c.ise the rem.jrkable fact was observed, that every other 

 pole escaped the discharge; and the same plienomenon vvas observed, 

 though in a less marked degree, near the H.ickensack River. In some 

 instances the lightning has been seen coursing along t!ie wire in a 

 stream of light; and in another case it is described as exploding from 

 the wire at certain points, though there were no bodies in the vicinity 

 to attract it from the conductor. 



In discussing these and other facts to be mentioned hereafter, we 

 shall, for convenience, adopt the [-rinciples and language of the theory 

 V* liicli refers the phenomena of electricity to the action of a fluid, of 

 which tlie particles repel each other, and are attracted bv the parti- 

 cles of other mdter. Although it cannot be affirmed that this theory 

 is an actual representation of the cause of the phenomena as they are 

 produced in nature, yet it may be assorted that it is, in the present 

 state ot science, an accurate mode of expressing the laws of electrical 

 action, so far as they have been made out ; and that though there are 

 a number of phenomena which have not as yet been referred to this 

 theory, there are none which are proved to be directly at variance 

 with it. 



That the wires of the telegraph should be freqiicnllv struck by a 

 direct discharge of lightning, is not surprising, when we consider the 

 great length of the conductor, and coiis.quently the many points along 

 the surface of the earth through which it must pass peculiarly liable 

 to receive the discharge from the heavens. Also, from the great 

 length of the conductor, the more readily must the repulsive action of 

 the free electricity of the cloud drive the natural electricity of the 

 conductor to tlie further end of the line, thus rendering more intense 

 the negative condition of the nearer part of the wire, and consequently 

 increasing the attraction ofthemctai for the free electricity of the 

 cloud. It is not however probable that the attraction, whatever may 

 belts intensity, of so small a quantity of m.itler as that of the wire of 

 the telegraph, can of itself produce an electrical discharge from the 

 heavens; aflhough, if the discharge were started by some other cause, 

 »uch as the attraclion of a large mass of conducting matter in the 

 vicinity, the attraction ot the wire might be sullicient to change the 

 direction of the descending bolt, and draw it in part or whole to it- 

 self. It should also be recollectt;d that, on account of the perfect 

 eanduclion, a discharge on any part of the wire must all'ect every 

 other part of the connected line, although it may be hundreds of miles 

 ID length. 



■ American PliUosopbical Society, IWo. 



That the wire should give off a discharge to a number of poles in 

 succession, is a fact I should have expected, fiom my previous re- 

 searches on the lateral discharge of a conductor traiisinitting a current 

 of free electrici'y. In a paper on this subject, presented to the Bri- 

 tish Association in 1S37, 1 showed that when electricity strikes a con- 

 ductor explosively, it tends to give off sparks to ail bodies in the 

 vicinity, however intimately the conductor may be connected with the 

 earth. In an experiment in which sparks from a small machine were 

 thrown on the upper part of a lightning-rod, erected in accordance 

 with th- formula given by the French Institute, corresponding sparks 

 could be drawn from every part of the rod, even from that near the 

 ground. In a cummunication since made to this Society, I have suc- 

 ceeded in referring this phenomenon to the fact, that during the trans- 

 mission of a quantity of electiicity along a rod, the surface of the con- 

 ductor is charged in succession, as it were, by a wave of the fluid, 

 which, when it arrives opposite a given point, tends to give otV a 

 spark to a neighbouring bi dy, for the sam" reason that the charged 

 conductor of the machine gives ofl' a spark under the aanie circum- 

 stances. 



It might at first be supposed that the rerlundant electricity of the 

 conductor would exhaust itself in giving off the first spark, and that a 

 second discharge could not lake pi. ice; but il should be observed, that 

 the wave of free electricity, in its passage, is const.intly attracted to 

 the wire by the portion of the uncharged conductor which immedi- 

 ately precedes its position at any time; and hence but a part of the 

 whole reduiid.int electricity is given off at one place; the velocity of 

 transmission of the wave as it p.isses the neiglibuuring body, and its 

 attraction for the wire, prevenling a full discliarge at any one place. 

 The intensity of the successive explosions is explained by nferring to 

 the fact, that the rtisch.irge from the clouds does not generally consist 

 of a single wave of elpctricity, but of a number of disci.. irges along 

 the same path in rapid succession, or of a continuous discliarge which 

 has an appreci.ible dur.ition ; and hence the wire of the telegraph is 

 capable of transmitting an immense quantity of the fluid thus distri- 

 buted over a great length of the conductor. 



The remarkible facts of the explosions of the electricity into the 

 air, and of the poles being struck in interrupted succession, find a 

 plausible explanation in au.'tlnT electrical principle which 1 have 

 established, namely, in all c.ises of the disturbance of the ecpnhbiiura 

 of the electrical plenum, which we must suppose to exist tliioughout 

 all terrestri.d space, the state of rest is attained by a series of dimi- 

 nishing oscillations. Thus in the discharge of a Leyd^n j.ir, I have 

 shown that the phenomena exhibited c miiot be expliiued by merely 

 supposing the transfer of .i quantity ol fluid from the inner to the outer 

 side of the j.ir ; but in addiiion to this we are obliged to admit the 

 existence of several waves, backw.irds and forwards, until the equili- 

 brium is attained. In the case of the disch.irge from the cloud, a 

 wave of the natural electrieily of the metal is repelled each w.iy from 

 the point on which the disch.irge falls, to either end of the wire, is 

 then n fleeted, and in its reverse passage meets in succession the 

 several w.ives which m.ike up the discliarge from the clou 1. These 

 waves will therefore interfere at cert.uii points along the wire, pro- 

 ducing, foi- a moment waves of double magnitude, and will thus en- 

 hance the tendency of the fluid at these poinls to fly from the con- 

 ductor. I do not say tli.it the eff._'cts observed were aclually produced 

 in this way ; I merely wish to convey the idea that known principles 

 of electrical action might, under certain circumstances, lead us to an- 

 ticipate such results. 



2. The state of the wire may be disturbed by the conduction of a 

 current of tlectricity from one portion of space to another, without 

 the presence of a thuuder-cloud ; and this will happen incase of a 

 long line, when the electrical condition of the atmosphere which sur- 

 rounds the wire at one place is difl'erent from that at another. Now 

 it is well known that a mere difference in elevation is attended with a 

 change ill the electrical state of the atmosphere. A conductor, ele- 

 vated bv means of a kite, gives sparks of positive electricity in a per- 

 fectly clear d.iy ; hence il the line of the telegraph passes over an 

 elevated mountain ridge, there will be continually, during clear 

 weather, a current from the more elevated to the lower points of the 

 conductor. 



A current may also be produced in a long level line, by the precipi- 

 tation of vapour in the foiin of fog at one end, while the air remains 

 clear at the other; or by the existence of a storm of rain or snow at 

 any point along the line, while the other parts of the wire are not 

 subjected to the same influence. 



Currents of sufficient power to set in motion the marking ma- 

 chine of the telegraph have been observed, which must have been 

 produced by some of these causes. In one case the luachine spon- 

 taneously began to operate without the aid of the battery, while a 



