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III. Experimental Researches in Electricity. — Ninth Series. By Michael Faraday, 
D.C.L. F.R.S. Fullerian Prof. Chem. Royal Institution, Corr. Memh, Royal and 
Imp. Acadd. of Sciences, Paris, Petersburgh, Florence, Copenhagen, Berlin, 8§c. 8$c. 

Received December 18, 1834, — Read January 29, 1835. 

§.15. On the influence by induction of an Electric Current on itself: — and 
on the inductive action of Electric Currents generally. 

1048. TlIE following investigations relate to a very remarkable inductive action 
of electric currents, or of the different parts of the same current, and indicate an 
immediate connexion between such inductive action and the direct transmission of 
electricity through conducting bodies, or even that exhibited in the form of a spark. 

1049. The inquiry arose out of a fact communicated to me by Mr. Jenkin, which 
is as follows. If an ordinary wire of short length be used as the medium of commu- 
nication between the two plates of an electromotor consisting of a single pair of 
metals, no management will enable the experimenter to obtain an electric shock from 
this wire ; but if the wire which surrounds an electro-magnet be used, a shock is 
felt each time the contact with the electromotor is broken, provided the ends of the 
wire be grasped one in each hand. 

1050. Another effect is observed at the same time, which has long been known to 
philosophers, namely, that a bright electric spark occurs at the place of disjunction. 

1051. A brief account of these results, with some of a corresponding character 
which I had observed in using long wires, was published in the Philosophical 
Magazine for 1834* ; and I added to them some observations on their nature. 
Further investigations led me to perceive the inaccuracy of my first notions, and 
ended in identifying these effects with the phenomena of induction which I had been 
fortunate enough to develop in the First Series of these Experimental Researches^. 
Notwithstanding this identity, the extension and the peculiarity of the views respect- 
ing electric currents which the results supply, lead me to believe that they will be 
found worthy of the attention of the Royal Society. 

1 052. The electromotor used consisted of a cylinder of zinc introduced between the 
two parts of a double cylinder of copper, and preserved from metallic contact in the 
usual way by corks. The zinc cylinder was eight inches high and four inches in 
diameter. Both it and the copper cylinder were supplied with stiff wires, surmounted 
by cups containing mercury ; and it was at these cups that the contacts of wires, he- 

* Vol. v. p. 349. t Philosophical Transactions, 1832, p. 126. 

MDCCCXXXV. G 



42 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

lices, or electro-magnets, used to complete the circuit, were made or broken. These 
cups I will call G and E throughout the rest of this paper (1079.). 

1053. Certain helices were constructed, some of which it will be necessary to de- 
scribe. A pasteboard tube had four copper wires, one twenty-fourth of an inch in 
thickness, wound round it, each forming a helix in the same direction from end to 
end : the convolutions of each wire were separated by string, and the superposed 
helices prevented from touching by intervening calico. The lengths of the wires 
forming the helices were 48, 49*5, 48, and 45 feet. The first and third wires were 
united together so as to form one consistent helix of 96 feet in length ; and the se- 
cond and fourth wires were similarly united to form a second helix, closely inter- 
woven with the first, and 94 - 5 feet in length. These helices may be distinguished by 
the numbers i and ii. They were carefully examined by a powerful current of electri- 
city and a galvanometer, and found to have no communication with each other. 

1054. Another helix was constructed upon a similar pasteboard tube, two lengths 
of the same copper wire being used, each forty-six feet long. These were united into 
one consistent helix of ninety-two feet, which therefore was nearly equal in value to 
either of the former helices, but was not in close inductive association with them. 
It may be distinguished by the number iii. 

1055. A fourth helix was constructed of very thick copper wire, being one fifth of 
an inch in diameter ; the length of wire used was seventy-nine feet, independently of 
the straight terminal portions. 

1056. The principal electro-magnet employed consisted of a cylindrical bar of soft 
iron twenty-five inches long, and one inch and three quarters in diameter, bent into 
a ring, so that the ends nearly touched, and surrounded by three coils of thick copper 
wire, the similar ends of which were fastened together ; then each of these termina- 
tions was soldered to a copper rod, serving as a conducting continuation of the wire. 
Hence any electric current sent through the rods was divided in the helices surround- 
ing the ring, into three parts, all of which, however, moved in the same direction. The 
three wires may therefore be considered as representing one wire, of thrice the thick- 
ness of the wire really used. 

1057- Other electro-magnets could be made at pleasure by introducing a soft iron 
rod into any of the helices described (1053. &c). 

1058. The galvanometer which I had occasion to use was rough in its construction, 
having but one magnetic needle, and not at all delicate in its indications. 

1059. The effects to be considered depend on the conductor employed to complete 
the communication between the zinc and copper plates of the electromotor ; and I 
shall have to consider this conductor under four different forms : as the helix of an 
electro-magnet (1056.) ; as an ordinary helix (1053. &c.) ; as a long extended wire, 
having its course such that the parts can exert no mutual influence ; and as a short 
wire. In all cases the conductor was of copper. 

1060. The effects are best shown by the electro-magnet (1056.). When it was 



INDUCTIVE ACTION OF AN ELECTRIC CURRENT ON ITSELF. 43 

used to complete the communication at the electromotor, there was no sensible 
spark on making contact, but on breaking contact there was a very large and bright 
spark, with considerable combustion of the mercury. Then, again, with respect to 
the shock : if the hands were moistened in salt and water, and good contact between 
them and the wires retained, no shock could be felt upon making contact at the elec- 
tromotor, but a powerful one on breaking contact. 

1061. When the helix i or iii (1053. &c.) was used as the connecting conductor, 
there was also a good spark on breaking contact, but none (sensibly) on making 
contact. On trying to obtain the shock from these helices, I could not succeed at 
first. By joining the similar ends of i and ii so as to make the two helices equivalent 
to one helix, having wire of double thickness, I could just obtain the sensation. Using 
the helix of thick wire (1055.) the shock was distinctly obtained. On placing the 
tongue between two plates of silver connected by wires with the parts which the 
hands had heretofore touched (1064.), there was a powerful shock on breaking con- 
tact, but none on making contact. 

1062. The power of producing these phenomena exists therefore in the simple helix, 
as in the electro-magnet, although by no means in the same high degree. 

1063. On putting a bar of soft iron into the helix, it became an electro-magnet 
(1057.), and its power was instantly and greatly raised. On putting a bar of copper 
into the helix, no change was produced, the action being that of the helix alone. The 
two helices i and ii, made into one helix of twofold length of wire, produced a greater 
effect than either i or ii alone. 

1064. On descending from the helix to the mere long wire, the following effects 
were obtained. A copper wire, 0*18 of an inch in diameter, and 132 feet in length, 
was laid out xipon the floor of the laboratory, and used as the connecting conductor 
(1059.) ; it gave no sensible spark on making contact, but produced a bright one on 
breaking contact, yet not so bright as that from the helix (1061.). On endeavouring 
to obtain the electric shock at the moment contact was broken, I could not succeed 
so as to make it pass through the hands ; but by using two silver plates fastened by 
small wires to the extremity of the principal wire used, and introducing the tongue 
between those plates, I succeeded in obtaining powerful shocks upon the parts of the 
mouth, and could easily convulse a flounder, an eel, or a frog. None of these effects 
could be obtained directly from the electromotor, i. e. when the tongue, frog, or fish 
was in a similar, and therefore comparative manner, interposed in the course of the 
communication between the zinc and copper plates, separated eveiywhere else by the 
acid used to excite the combination. The bright spark and the shock, produced only 
on breaking contact, are therefore effects of the same kind as those produced in a 
higher degree by the helix, and in a still higher degree by the electro-magnet. 

1065. In order to compare an extended wire with a helix, the helix i, containing 
ninety-six feet, and ninety-six feet of the same- sized wire lying on the floor of the 
laboratory, were used alternately as conductors: the former gave a much brighter 

g2 



44 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

spark at the moment of disjunction than the latter. Again, twenty-eight feet of cop- 
per wire were made up into a helix, and being used gave a good spark on disjunction 
with the electromotor ; being then suddenly pulled out and again employed, it gave a 
much smaller spark than before, although nothing but its spiral arrangement had 
been changed. 

1066. As the superiority of a helix over a wire is important to the philosophy of 
the effect, I took particular pains to ascertain the fact with certainty. A wire of cop- 
per sixty-seven feet long was bent in the middle so as to form a double termination 
which could be communicated with the electromotor ; one of the halves of this wire 
was made into a helix and the other remained in its extended condition. When these 
were used alternately as the connecting wire, the helix gave by much the strongest 
spark. It even gave a stronger spark than when it and the extended wire were used 
conjointly as a double conductor. 

1067. When a short wire is used, all these effects disappear. If it be only two or 
three inches long, a spark can scarcely be perceived on breaking the junction. If it 
be ten or twelve inches long and moderately thick, a small spark may be more easily 
obtained. As the length is increased, the spark becomes proportionately brighter, until 
from extreme length the resistance offered by the metal as a conductor begins to in- 
terfere with the principal result. 

1068. The effect of elongation was well shown thus : 114 feet of copper wire, one 
eighteenth of an inch in diameter, were extended on the floor and used as a conduc- 
tor ; it remained cold, but gave a bright spark on breaking contact. Being crossed so 
that the two terminations were in contact near the extremities, it was again used as 
a conductor, only twelve inches now being included in the circuit : the wire became 
very hot from the greater quantity of electricity passing through it, and yet the spark 
on breaking contact was scarcely visible. The experiment was repeated with a wire 
one ninth of an inch in diameter and thirty-six feet long with the same results. 

1069. That the effects, and also the action, in all these forms of the experiment are 
identical ; is evident from the manner in which the former can be gradually raised from 
that produced by the shortest wire to that of the most powerful electro-magnet : and 
this capability of examining what will happen by the most powerful apparatus, and 
then experimenting for the same results, or reasoning from them, with the weaker ar- 
rangements, is of great advantage in making out the true principles of the phenomena. 

1 070. The action is evidently dependent upon the wire which serves as a con- 
ductor ; for it varies as that wire varies in its length or arrangement. The shortest 
wire may be considered as exhibiting the full effect of spark or shock which the 
electromotor can produce by its own direct power ; all the additional force which 
the arrangements described can excite being due to some affection of the current, 
either permanent or momentary, in the wire itself. That it is a momentary effect, pro- 
duced only at the instant of breaking contact, will be fully proved (1089. 1100.). 

1071. No change takes place in the quantity or intensity of the current during the 



THE CONSTANT CURRENT UNCHANGED IN ITS CHARACTERS. 45 

time the latter is continued, from the moment after contact is made up to that pre- 
vious to disunion, except what depends upon the increased obstruction offered to 
the passage of the electricity by a long wire as compared to a short wire. To ascer- 
tain this point with regard to quantity, the helix i (1053.) and the galvanometer 
(1058.) were both made parts of the metallic circuit used to connect the plates of a 
small electromotor, and the deflection at the galvanometer was observed ; then a soft 
iron core was put into the helix, and as soon as the momentary effect was over, and 
the needle had become stationary, it was again observed, and found to stand exactly 
at the same division as before. Thus the quantity passing through the wire when 
the current was continued was the same either with or without the soft iron, although 
the peculiar effects occurring at the moment of disjunction were very different in de- 
gree under such variation of circumstances. 

1072. That the quality of intensity belonging to the constant current did not vary 
with the circumstances favouring the peculiar results under consideration, so as to 
yield an explanation of those results, was ascertained in the following manner. The 
current excited by an electromotor was passed through short wires, and its intensity 
tried by subjecting different substances to its electrolyzing power (912. 966. &c.) ; it 
was then passed through the wires of the powerful electro-magnet (1056.), and again 
examined with respect to its intensity by the same means and found unchanged. 
Again, the constancy of the quantity passed in the above experiment (1071.) adds 
further proof that the intensity could not have varied ; for had it been increased upon 
the introduction of the soft iron, there is every reason to believe that the quantity 
passed in a given time would also have increased. 

1073. The fact is, that under many variations of the experiments, the permanent 
current loses in force as the effects upon breaking contact become exalted. This is 
abundantly evident in the comparative experiments with long and short wires (1068); 
and is still more strikingly shown by the following variation. Solder an inch or two 
in length of fine platina wire (about one hundredth of an inch in diameter) on to one 
end of the long communicating wire, and also a similar length of the same platina 
wire on to one end of the short communication ; then, in comparing the effects of these 
two communications, make and break contact between the platina terminations and 
the mercury of the cup G or E (1079.). When the short wire is used, the platina will 
be ignited by the constant current, because of the quantity of electricity, but the 
spark on breaking contact will be hardly visible ; on using the longer communicating 
wire, which by obstructing will diminish the current, the platina will remain cold 
whilst the current passes, but give a bright spark at the moment it ceases : thus the 
strange result is obtained of a diminished spark and shock from the strong current, 
and increased effects from the weak one. Hence the spark and shock at the moment 
of disjunction, although resulting from great intensity and quantity of the current at 
that moment, are no direct indicators or measurers of the intensity or quantity of the 
constant current previously passing, and by which they are ultimately produced. 



46 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

1074. It is highly important in using the spark as an indication, by its relative 
brightness, of these effects, to bear in mind certain circumstances connected with its 
production and appearance. An ordinary electric spark is understood to be the bright 
appearance of electricity passing suddenly through an interval of air, or other badly 
conducting matter. A voltaic spark is sometimes of the same nature, but, generally, 
is due to the ignition and even combustion of a minute portion of a good conductor ; 
and that is especially the case when the electromotor consists of but one or few pairs 
of plates. This can be very well observed if either or both of the metallic surfaces 
intended to touch be solid and pointed. The moment they come in contact the cur- 
rent passes ; it heats, ignites, and even burns the touching points, and the appearance 
is as if the spark passed on making contact, whereas it is only a case of ignition by 
the current, contact being previously made, and is perfectly analogous to the ignition 
of a fine platina wire connecting the extremities of a voltaic battery. 

1075. When mercury constitutes one or both of the surfaces used, the brightness of 
the spark is greatly increased. But as this effect is due to the action on, and probable 
combustion of, the metal, such sparks must only be compared with other sparks also 
taken from mercurial surfaces, and not with such as may be taken, for instance, be- 
tween surfaces of platina or gold, for then the appearances are far less bright, though 
the same quantity of electricity be passed. It is not at all unlikely that the com- 
monly occurring circumstance of combustion may affect even the duration of the 
light ; and that sparks taken between mercury, copper, or other combustible bodies, 
will continue for a period sensibly longer than those passing between platina or gold. 

1076. When the end of a short clean copper wire, attached to one plate of an 
electromotor, is brought down carefully upon a surface of mercury connected with 
the other plate, a spark, almost continuous, can be obtained. This I refer to a succes- 
sion of effects of the following nature : first contact, — then ignition of the touching 
points, — recession of the mercury from the mechanical results of the heat produced at 
the place of contact, and the electro-magnetic condition of the parts at the moment*, 
— breaking of the contact and the production of the peculiar intense effect dependent 
thereon, — renewal of the contact by the returning surface of the undulating mercury, 
— and then a repetition of the same series of effects, and that with such rapidity as to 
present the appearance of a continued discharge. If a long wire or an electro-magnet 
be used as the connecting conductor instead of a short wire, a similar appearance may 
be produced by tapping the vessel containing the mercury and making it vibrate ; but 
the sparks do not usually follow each other so rapidly as to produce an apparently 
continuous spark, because of the time required when the long wire or electro-magnet 
is used both for the full development of the current (1101. 1106.) and for its complete 
cessation. 

1077- Returning to the phenomena in question, the first thought that arises in the 
mind is, that the electricity circulates with something like momentum or inertia in 

* Quarterly Journal of Science, vol. xii. p. 420. 



INDUCTIVE ACTION OF A CURRENT UPON ITSELF. 47 

the wire, and that thus a long wire produces effects at the instant the current is 
stopped, which a short wire cannot produce. Such an explanation is, however, at 
once set aside by the fact, that the same length of wire produces the effects in very 
different degrees, according as it is simply extended, or made into a helix, or forms 
the circuit of an electro-magnet (1069.). The experiments to be adduced (1089.) 
will still more strikingly show that the idea of momentum cannot apply. 

1078. The bright spark at the electromotor, and the shock in the arms, appeared 
evidently to be due to one current in the long wire, divided into two parts by the 
double channel afforded through the body and through the electromotor ; for that 
the spark was evolved at the place of disjunction with the electromotor, not by any 
direct action of the latter, but by a force immediately exerted in the wire of commu- 
nication, seemed to be without doubt (1070.). It followed, therefore, that by using 
a better conductor in place of the human body, the whole of this extra current might 
be made to pass at that place ; and thus be separated from that which the electro- 
motor could produce by its immediate action, and its direction be examined apart 
from any interference of the original and originating current. This was found to be 
true ; for on connecting the ends of the principal wire together by a cross wire two 
or three feet in length, applied just where the hands had felt the shock, the whole of 
the extra current passed by the new channel, and then no better spark than one 
producible by a short wire was obtained on disjunction at the electromotor. 

1079. The current thus separated was examined by galvanometers and decom- 
posing apparatus introduced into the course of this wire. I will always speak of it 
as the current in the cross wire or wires, so that no mistake, as to its place or ori- 
gin, may occur. In the wood-cut, Z and C represent the zinc and r \ 

copper plates of the electromotor ; G and E the cups of mercury y- V ^ 

where contact is made or broken (1052.) ; A and B the termina- 
tions of D the long wire, the helix, or the electro-magnet, used to 
complete the circuit ; N and P are the cross wires, which can 
either be brought into contact at x, or else have a galvanometer 
(1058.) or an electrolyzing apparatus (312. 316.) interposed there. 

The production of the shock from the current in the cross wire, 
whether D was a long extended wire, or a helix, or an electro-magnet, has been 
already described (1064. 1061. 1060.). 

1080. The spark of the cross-wire current could be produced at w in the following 
manner : D was made an electro-magnet ; the metallic extremities at x were held 
close together, or rubbed lightly against each other, whilst contact was broken at 
G or E. When the communication was perfect at x, little or no spark appeared at 
G or E. When the condition of vicinity at x was favourable for the result required, 
a bright spark would pass there at the moment of disjunction, none occurring at G 
and E : this spark was the luminous passage of the extra current through the cross- 
wires. When there was no contact or passage of current at op, then the spark ap- 



48 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

peared at G or E, the extra current forcing its way through the electromotor itself. 
The same results were obtained by the use of the helix or the extended wire at D in 
place of the electro-magnet. 

1081. On introducing a fine platina wire at <r, and employing the electro-magnet 
at D, no visible effects occurred as long as contact was continued ; but on breaking 
contact at G or E, the fine wire was instantly ignited and fused. A longer or thicker 
wire could be so adjusted at x as to show ignition, without fusion, every time the 
contact was broken at G or E. 

1082. It is rather difficult to obtain this effect with helices or wires, and for very 
simple reasons : with the helices i, ii, or iii, there was such retardation of the elec- 
tric current, from the length of wire used, that a full inch of platina wire one fiftieth 
of an inch in diameter could be retained ignited at the cross wires during the con- 
tinuance of contact, by the portion of electricity passing through it. Hence it was 
impossible to distinguish the particular effects at the moments of making or breaking 
contact from this constant effect. 

1083. On using the thick wire helix (1055.), the same results ensued. Proceeding, 
however, upon the known fact that electric currents of great quantity but low inten- 
sity, though able to ignite thick wires, cannot produce that effect upon thin ones, I 
used a very fine platina wire at x, reducing its diameter until a spark appeared at G 
or E, when contact was broken there. A quarter of an inch of such wire might be 
introduced at x without being ignited by the continuance of contact at G or E ; but 
when contact was broken at either place, this wire became red hot ; proving, by this 
method, the production of the induced current at that moment. 

1084. Chemical decomposition was next effected by the cross- wire current, an elec- 
tro-magnet being used at D, and a decomposing apparatus, with solution of iodide of 
potassium in paper (1079.), employed at x. The conducting power of the connecting 
system A B D was sufficient to carry all the primary current, and consequently no 
chemical action took place at x during the continuance of contact at G and E ; but 
when contact was broken, there was instantly decomposition at x. The iodine 
appeared against the wire N, and not against the wire P ; thus demonstrating that 
the current through the cross-wires, when contact was broken, was in the reverse 
direction to that marked by the arrow, or that which the electromotor would have 
sent through it. 

1085. In this experiment a bright spark occurs at the place of disjunction, indi- 
cating that only a small part of the extra current passed the apparatus at x, because 
of the small conducting power of the latter. 

1086. I found it difficult to obtain the chemical effects with the simple helices and 
wires, in consequence of the diminished inductive power of these arrangements, and 
because of the passage of a strong constant current at x whenever a very active 
electromotor was used (1082.). 

1087. The most instructive set of results was obtained, however, when the galvano- 



INDUCTIVE ACTION OF AN ELECTRIC CURRENT. 49 

meter was introduced at oc. Using an electro- magnet at D, and continuing contact, 
a current was then indicated by the deflection, proceeding from P to N, in the direc- 
tion of the arrow ; the cross wire serving to carry one part of the electricity excited 
by the electromotor, and the arrangement A B D, as indicated by the arrows, the 
other and far greater part. The magnetic needle was then forced back, by pins 
applied upon opposite sides of its two extremities, to its natural position when unin- 
fluenced by a current ; after which, contact being broken at G or E, it was deflected 
strongly in the opposite direction ; thus showing, in accordance with the chemical 
effects (1084.), that the extra current followed a course in the cross wires contrary to 
that indicated by the arrow, i. e. the one produced by the direct action of the elec- 
tromotor *. 

1088. With the helix only, these effects could scarcely be observed, in consequence 
of the smaller inductive force of this arrangement, the opposed action from induc- 
tion in the galvanometer wire itself, the mechanical condition and tension of the 
needle from the effect of blocking (1087.) whilst the current due to continuance of 
contact was passing round it, and other causes. With the extended wire all these cir- 
cumstances had still greater influence, and therefore allowed less chance of success. 

1089. These experiments, establishing as they did, by the quantity, intensity, and 
even direction, a distinction between the primary or generating current and the extra 
current, led me to conclude that the latter was identical with the induced current 
described (6. 26.) in the first series of these Researches ; and this opinion I was soon 
able to bring to proof, and at the same times obtained not the partial (1078.) but 
entire separation of one current from the other. 

1090. The double helix (1053.) was arranged so that i should form the connecting 
wire between the plates of the electromotor, ii being out of the current, and its ends 
unconnected. In this condition i acted very well, and gave a good spark at the time 
and place of disjunction. The opposite ends of ii were then connected together so as 
to form an endless wire, i remaining unchanged : but now no spark, or one scarcely 
sensible, could be obtained from the latter at the place of disjunction. Then, again, 
the ends of ii were held so nearly together that any current running round that helix 
should be rendered visible as a spark ; and in this manner a spark was obtained from 
ii when the junction of i with the electromotor was broken, in place of appearing at 
the disjoined extremity of i itself. 

1091. By introducing a galvanometer or a decomposing apparatus into the circuit 
formed by the helix ii, I could easily obtain the deflections and decomposition oc- 
casioned by the induced current due to the breaking contact at helix i, or even to 
that occasioned by making contact of that helix with the electromotor ; the results in 
both cases indicating the contrary directions of the two induced currents thus pro- 
duced (26.). 

* It was ascertained experimentally, that if a strong current was passed through the galvanometer only, and 
the needle restrained in one direction as above in its natural position, when the current was stopped, no viora- 
tion of the needle in the opposite direction took place. 
MDCCCXXXV. H 



50 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

1092. All these effects, except those of decomposition, were reproduced by two ex- 
tended long wires, not having the form of helices, but placed close to each other ; and 
thus it was proved that the extra current could be removed from the wire carrying 
the original current to a neighbouring wire, and was at the same time identified, in 
direction and every other respect, with the currents producible by induction (1089.). 
The case, therefore, of the bright spark and shock on disjunction may now be stated 
thus : If a current be established in a wire, and another wire, forming a complete cir- 
cuit, be placed parallel to the first, at the moment the current in the first is stopped it 
induces a current in the same direction in the second, the first exhibiting then but a 
feeble spark ; but if the second wire be away, disjunction of the first wire induces a 
current in itself in the same direction, producing a strong spark. The strong spark 
in the single long wire or helix, at the moment of disjunction, is therefore the equiva- 
lent of the current which would be produced in a neighbouring wire if such second 
current were permitted. 

1093. Viewing the phenomena as the results of the induction of electrical currents, 
many of the principles of action, in the former experiments, become far more evident 
and precise. Thus the different effects of short wires, long wires, helices, and elec- 
tro-magnets (1069.) may be comprehended. If the inductive action of a wire a foot 
long upon a collateral wire also a foot in length, be observed, it will be found very 
small ; but if the same current be sent through a wire fifty feet long, it will induce in 
a neighbouring wire of fifty feet a far more powerful current at the moment of making 
or breaking contact, each successive foot of wire adding to the sum of action ; and 
by parity of reasoning, a similar effect should take place when the conducting wire 
is also that in which the induced current is formed : hence the reason why a long 
wire gives a brighter spark on breaking contact than a short one (1068.), although 
it carries much less electricity. 

1094. If the long wire be made into a helix, it will then be still more effective in 
producing sparks and shocks on breaking contact ; for by the mutual inductive action 
of the convolutions each aids its neighbour, and will be aided in turn, and the sum 
of effect will be very greatly increased. 

1095. If an electro-magnet be employed, the effect will be still more highly ex- 
alted ; because the iron, magnetized by the power of the continuing current, will 
lose its magnetism at the moment the current ceases to pass, and in so doing will 
tend to produce an electric current in the wire around it (37-38.), in conformity with 
that which the cessation of current in the helix itself also tends to produce. 

1096. By applying the laws of the induction of electric currents formerly deve- 
loped (6. &c), various new conditions of the experiments could be devised, which by 
their results should serve as tests of the accuracy of the view just given. Thus, if a 
long wire be doubled, so that the current in the two halves shall have opposite actions, 
it ought not to give a sensible spark at the moment of disjunction : and this proved 
to be the case, for a wire forty feet long, covered with silk, being doubled and tied 
closely together to within four inches of the extremities, when used in that state, 



INDUCTIVE ACTION OF AN ELECTRIC CURRENT. 51 

gave scarcely a perceptible spark ; but being opened out and the parts separated, it 
gave a very good one. The two helices i and ii being joined at their similar ends, 
and then used at their other extremities to connect the plates of the electromotor, 
thus constituted one long helix, of which one half was opposed in direction to the 
other half: under these circumstances it gave scarcely a sensible spark, even when 
the soft iron core was within, although containing nearly two hundred feet of wire. 
When it was made into one consistent helix of the same length of wire it gave a very 
bright spark. 

1097- Similar proofs can be drawn from the mutual inductive action of two sepa- 
rate currents (1110.); and it is important for the general principles that the consist- 
ent action of two such currents should be established. Thus, two currents going in 
the same direction should, if simultaneously stopped, aid each other by their relative 
influence ; or if proceeding in contrary directions, should oppose each other under 
similar circumstances. I endeavoured at first to obtain two currents from two dif- 
ferent electromotors, and passing them through the helices i and ii, tried to effect 
the disjunctions mechanically at the same moment. But in this I could not suc- 
ceed ; one was always separated before the other, and in that case produced little or 
no spark, its inductive power being employed in throwing a current round the re- 
maining complete circuit (1090.) : the current which was stopped last always gave a 
bright spark. If it were ever to become needful to ascertain whether two junctions 
were accurately broken at the same moment, these sparks would afford a test for the 
purpose, having an infinite degree of perfection. 

1098. I was able to prove the points by other expedients. Two short thick wires 
were selected to serve as terminations, by which contact could be made or broken 
with the electromotor. The compound helix, consisting of i and ii (1053.), was ad- 
justed so that the extremities of the two helices could be placed in communication 
with the two terminal wires, in such a manner that the current moving through the 
thick wires should be divided into two equal portions in the two helices, these por- 
tions travelling, according to the mode of connexion, either in the same direction 
or in contrary directions at pleasure. In this manner two streams could be obtained, 
both of which could be stopped simultaneously, because the disjunction could be 
broken at G or F by removing a single wire. When the helices were in contrary 
directions, there was scarcely a sensible spark at the place of disjunction ; but when 
they were in accordance there was a very bright one. 

1099. The helix i was now used constantly, being sometimes associated, as above, 
with helix ii in an according direction, and sometimes with helix iii, which was placed 
at a little distance. The association i and ii, which presented two currents able to 
affect each other by induction, because of their vicinity, gave a brighter spark than 
the association i and iii, where the two streams could not exert their mutual in- 
fluence ; but the difference was not so great as I expected. 

1 100. Thus all the phenomena tend to prove that the effects are due to an induc- 

h 2 



52 DR. FARADAY'S EXPERLYIENTAL RESEARCHES IN ELECTRICITY. 

tive action, occurring at the moment when the principal current is stopped. I at one 
time thought they were due to an action continued during the continuance of the 
current, and expected that a steel magnet would have an influence according to its 
position in the helix, comparable to that of a soft iron bar, in assisting the effect. 
This, however, is not the case ; for hard steel, or a magnet in the helix, is not so ef- 
fectual as soft iron; nor does it make any difference how the magnet is placed in the 
helix, and for very simple reasons, namely, that the effect does not depend upon a 
permanent state of the core, but a change of state, and that the magnet or hard steel 
cannot sink through such a difference of state as soft iron, at the moment contact 
ceases, and therefore cannot produce an equal effect in generating a current of elec- 
tricity by induction (34. 37.). 



1101. As an electric current acts by induction with equal energy at the moment 
of its commencement as at the moment of its cessation (10. 26.), but in a contrary 
direction, the reference of the effects under examination to an inductive action, would 
lead to the conclusion that corresponding effects of an opposite nature must occur 
in a long wire, a helix, or an electro-magnet, every time that contact is made with the 
electromotor. These effects will tend to establish a resistance for the first moment 
in the long conductor, producing a result equivalent to the reverse of a shock or a 
spark. Now it is very difficult to devise means fit for the recognition of such nega- 
tive results ; but as it is probable that some positive effect is produced at the time, 
if we knew what to expect, I think the few facts bearing upon this subject with which 
I am acquainted are worth recording. 

1102. The electro-magnet was arranged with an electrolyzing apparatus at x, as 
before described (1084.), except that the intensity of the chemical action at the elec- 
tromotor was increased until the electric current was just able to produce the feeblest 
signs of decomposition whilst contact was continued at G and E (1079.) ; (the iodine 
of course appearing against the end of the cross wire P ;) the wire N was also sepa- 
rated from A at r, so that contact there could be made or broken at pleasure. Under 
these circumstances the following set of actions was repeated several times : contact 
was broken at r, then broken at G, next made at r, and lastly renewed at G ; thus 
any current from N to P due to breaking of contact was avoided, but any additional 
force to the current from P to N due to making contact could be observed. In this 
way it was found, that a much greater decomposing effect (causing the evolution of 
iodine against P) could be obtained by a few completions of contact than by the cur- 
rent which could pass in a much longer time if the contact was continued. This I 
attribute to the act of induction in the wire ABDat the moment of contact render- 
ing that wire a worse conductor, or rather retarding the passage of the electricity 
through it for the instant, and so throwing a greater quantity of the electricity which 
the electromotor could produce, through the cross wire passage N P. The instant 
the induction ceased, ABD resumed its full power of carrying a constant current of 



INDUCTIVE EFFECT AT THE COMMENCEMENT OF A CURRENT. 53 

electricity, and could have it highly increased, as we know by the former experi- 
ments (1060.) by the opposite inductive action brought into activity at the moment 
contact at Z or C was broken. 

1103. A galvanometer was then introduced at oo, and the deflection of the needle 
noted whilst contact was continued at G and E : the needle was then blocked as 
before in one direction (1087-), so that it should not return when the current ceased, 
but remain in the position in which the current could retain it. Contact at G or E 
was broken, producing of course no visible effect ; it was then renewed, and the nee- 
dle was instantly deflected, passing from the blocking-pins to a position still further 
from its natural place than that which the constant current could give, and thus 
showing by the temporary excess of current in this cross communication, the tempo- 
rary retardation in the circuit ABD. 

1104. On adjusting a platina wire at x (1081.) so that it should not be ignited by 
the current passing through it whilst contact at G and E was continued, and yet be- 
come red hot by a current somewhat more powerful, I was readily able to produce 
its ignition upon making contact, and again upon breaking contact. Thus the momen- 
tary retardation in AB D on making contact was again shown by this result, as well 
also as the opposite result upon breaking contact. The two ignitions of the wire at x 
were of course produced by electric currents moving in opposite directions. 

1105. Using the helix only, I could not obtain distinct deflections at x, due to the 
extra effect on making contact, for the reasons already mentioned (1088.). By using 
a very fine platina wire there (1083.), I did succeed in obtaining the igniting effect 
for making contact in the same manner, though by no means to the same degree, as 
with the electro-magnet (1104.). 

1106. We may also consider and estimate the effect on making contact, by trans- 
ferring the force of induction from the wire carrying the original current to a lateral 
wire, as in the cases described (1090.) ; and we then are sure, both by the chemi- 
cal and galvanometrical results (1091.), that the forces upon making and breaking 
contact, like action and reaction, are equal in their strength but contrary in their 
direction. If, therefore, the effect on making contact resolves itself into a mere re- 
tardation of the current at the first moment of its existence, it must be, in its degree, 
equivalent to the high exaltation of that same current at the moment contact is broken. 

1107- Thus the case, under the circumstances, is, that the intensity and quantity 
of electricity moving in a current are smaller when the current commences or is 
increased, and greater when it diminishes or ceases, than they would be if the in- 
ductive action occurring at these moments did not take place; or than they are in the 
original current wire if the inductive action be transferred from that wire to a colla- 
teral one (1090.). 

1108. From the facility of transference to neighbouring wires, and from the effects 
generally, the inductive forces appear to be lateral, i. e. exerted in a direction per- 
pendicular to the direction of the originating and produced currents : and they also 



54 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

appear to be accurately represented by the magnetic curves, and closely related to, 
if not identical with, magnetic forces. 

1109. There can be no doubt that the current in one part of a wire can act by in- 
duction upon other parts of the same wire which are lateral to the first, i. e. in the 
same section, or in the parts which are more or less oblique to it (1112.), just as it 
can act in producing a current in a neighbouring wire. It is this which gives the 
appearance of the current acting upon itself: but all the experiments and all analogy 
tend to show that the elements (if I may so say) of the currents do not act upon them- 
selves, and so cause the effect in question, but produce it by exciting currents in con- 
ducting matter which is lateral to them. 

1110. It is possible that some of the expressions I have used may seem to imply, 
that the inductive action is essentially the action of one current upon another, or of 
one element of a current upon another element of the same current. To avoid any 
such conclusion I must explain more distinctly my meaning. If an endless wire be 
taken, we have the means of generating a current in it which shall run round the 
circuit without adding any electricity to what was previously in the wire. As far as 
we can judge, the electricity which appears as a current is the same as that which 
before was quiescent in the wire ; and though we cannot as yet point out the essential 
condition of difference of the electricity at such times, we can easily recognise the two 
states. Now when a current acts by induction upon conducting matter lateral to it, 
it probably acts upon the electricity in that conducting matter whether it be in the 
form of a current or quiescent, in the one case increasing or diminishing the current 
according to its direction, in the other producing a current, and the amount of the 
inductive action is probably the same in both cases. Hence, to say that the action 
of induction depended upon the mutual relation of two or more currents, would, ac- 
cording to the restricted sense in which the term current is understood at present 
(283. 517. 667.), be an error. 

1111. Several of the effects, as, for instances, those with helices (1 066.), with accord- 
ing or counter currents (1097. 1098.), and those on the production of lateral cur- 
rents (1090.), appeared to indicate that a current could produce an effect of induction 
in a neighbouring wire more readily than in its own carrying wire, in which case it 
might be expected that some variation of result would be produced if a bundle of 
wires were used as a conductor instead of a single wire. In consequence the follow- 
ing experiments were made. A copper wire one twenty-third of an inch in diameter 
was cut into lengths of five feet each, and six of these being laid side by side in one 
bundle, had their opposite extremities soldered to two terminal pieces of copper. 
This arrangement could be used as a discharging wire, but the general current could 
be divided into six parallel streams, which might be brought close together, or, by 
the separation of the wires, be taken more or less out of each other's influence. A 
somewhat brighter spark was, I think, obtained on breaking contact when the six 
wires were close together than when held asunder. 



INDUCTIVE ACTION OP AN ELECTRIC CURRENT. 55 

1112. Another bundle, containing twenty of these wires, was eighteen feet long: 
the terminal pieces were one fifth of an inch in diameter, and each six inches long. 
This was compared with nineteen feet in length of copper wire one fifth of an inch in 
diameter. The bundle gave a smaller spark on breaking contact than the latter, even 
when its strands were held together by string : when they were separated, it gave a 
still smaller spark, Upon the whole, however, the diminution of effect was not such 
as I expected ; and I doubt whether the results can be considered as any proof of 
the truth of the supposition which gave rise to them. 

1113. The inductive force by which two elements of one current (1109. 1110.) act 
upon each other, appears to diminish as the line joining them becomes oblique to the 
direction of the current, and to vanish entirely when it is parallel. I am led by some 
results to suspect that it then even passes into the repulsive force noticed by Ampere* ; 
which is the cause of the elevations in mercury described by Sir Humphry Davy -f, 
and which again is probably directly connected with the quality of intensity. 

1114. Notwithstanding that the effects appear only at the making and breaking of 
contact, (the current remaining unaffected, seemingly, in the interval,) I cannot resist 
the impression that there is some connected and correspondent effect produced by 
this lateral action of the elements of the electric stream during the time of its conti- 
nuance (60. 242.). An action of this kind, in fact, is evident in the magnetic relations 
of the parts of the current. But admitting (as we may do for the moment) the mag- 
netic forces to constitute the power which produces such striking and different results 
at the commencement and termination of a current, still there appears to be a link in 
the chain of effects, a wheel in the physical mechanism of the action, as yet unrecog- 
nised. If we endeavour to consider electricity and magnetism as the results of two 
forces of a physical agent, or a peculiar condition of matter, exerted in determinate 
directions perpendicular to each other, then, it appears to me, that we must consider 
these two states or forces as convertible into each other in a greater or smaller degree ; 
i. e. that an element of an electric current has not a determinate electric force and a 
determinate magnetic force constantly existing in the same ratio, but that the two 
forces are, to a certain degree, convertible by a process or change of condition at pre- 
sent unknown to us. How else can a current of a given intensity and quantity be 
able, by its direct action, to sustain a state which, when allowed to react, (at the ces- 
sation of the original current,) shall produce a second current, having an intensity 
and quantity far greater than the generating one ? This cannot result from a direct 
reaction of the electric force ; and if it result from a change of electrical into mag- 
netic force, and a reconversion back again, it will show that they differ in some- 
thing more than mere direction, as regards that agent in the conducting wire which 
constitutes their immediate cause. 

1 115. With reference to the appearance, at different times, of the contrary effects 

* Recueil d' Observations Electro-Dynaniiques, p. 285. 
f Philosophical Transactions, 1823, p. 155. 



56 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 

produced by the making and breaking contact, and their separation by an inter- 
mediate and indifferent state, this separation is probably more apparent than real. 
If the conduction of electricity be effected by vibrations, or by any other mode in 
which opposite forces are successively and rapidly excited and neutralized, then we 
might expect a peculiar and contrary development of force at the commencement and 
termination of the periods during which the conducting action should last (somewhat 
in analogy with the colours produced at the outside of an imperfectly developed solar 
spectrum) : and the intermediate actions, although not sensible in the same way, may 
constitute the very essence of conductibility. It is by views and reasons such as these, 
which seem to me connected with the fundamental laws and facts of electrical science, 
that I have been induced to enter, more minutely than I otherwise should have done, 
into the experimental examination of the phenomena described in this paper. 

1116. Before concluding, I may briefly remai'k, that on using a voltaic battery of 
fifty pairs of plates instead of a single pair (1052.), the effects were exactly of the 
same kind. The spark on making contact, for the reasons before given, was very 
small (1101. 1107.); that on breaking contact, very excellent and brilliant. The 
continuous discharge did not seem altered in character, whether a short wire or the 
powerful electro-magnet were used as a connecting discharger. 

1117- The effects produced at the commencement and end of a current, (which are 
separated by an interval of time when that current is supplied from a voltaic appara- 
tus,) must occur at the same moment when a common electric discharge is passed 
through a long wire. Whether, if happening accurately at the same moment, they 
would entirely neutralize each other, or whether they would not still give some defi- 
nite peculiarity to the discharge, is a matter remaining to be examined ; but it is 
very probable that the peculiar character and pungency of sparks drawn from a long 
wire depend in part upon the increased intensity given at the termination of the dis- 
charge by the inductive action then occurring. 

1118. In the wire of the helix of magneto-electric machines, (as, for instance, in 
Mr. Saxton's beautiful arrangement,) an important influence of these principles of 
action is evidently shown. From the construction of the apparatus the current is per- 
mitted to move in a complete metallic circuit of great length during the first instants 
of its formation : it gradually rises in strength, and is then suddenly stopped by the 
breaking of the metallic circuit ; and thus great intensity is given by induction to the 
electricity, which at that moment passes (1064. 1060.). This intensity is not only 
shown by the brilliancy of the spark and the strength of the shock, but also by the 
necessity which has been experienced of well insulating the convolutions of the helix, 
in which the current is formed ; and it gives to the current a force at these moments 
very far above that which the apparatus could produce if the principle which forms 
the subject of this paper were not called into play. 

Royal Institution, 
December 8th, 1834.