varnished glass tube being directed sideways towards the ball, air was
sometimes blown through it at the ball and sometimes not. In the former
case, the place of the glow was changed a little, as if it were blown away
by the current, and this is just the result which might have been
anticipated. All these effects illustrate beautifully the general causes
and relations, both of the glow and the current of air accompanying it
(1574.).
1580. Flame facilitates the production of a current in the dielectric
surrounding it. Thus, if a ball which would not occasion a current in the
air have a flame, whether large or small, formed on its surface, the
current is produced with the greatest ease; but not the least difficulty
can occur in comprehending the effective action of the flame in this case,
if its relation, as part of the surrounding dielectric, to the electrified
ball, be but for a moment considered (1375. 1380.).
1581. Conducting fluid terminations, instead of rigid points, illustrate in
a very beautiful manner the formation of the currents, with their effects
and influence in exalting the conditions under which they were commenced.
Let the rounded end of a brass rod, 0.3 of an inch or thereabouts in
diameter, point downwards in free air; let it be amalgamated, and have a
drop of mercury suspended from it; and then let it be powerfully
electrized. The mercury will present the phenomenon of _glow_; a current of
air will rush along the rod, and set off from the mercury directly
downwards; and the form of the metallic drop will be slightly affected, the
convexity at a small part near the middle and lower part becoming greater,
whilst it diminishes all round at places a little removed from this spot.
The change is from the form of _a_ (fig. 135.) to that of _b_, and is due
almost, if not entirely, to the mechanical force of the current of air
sweeping over its surface.
1582. As a comparative observation, let it be noticed, that a ball
gradually brought towards it converts the glow into brushes, and ultimately
sparks pass from the most projecting part of the mercury. A point does the
same, but at much smaller distances.
1583. Take next a drop of strong solution of muriate of lime; being
electrified, a part will probably be dissipated, but a considerable
portion, if the electricity be not too powerful, will remain, forming a
conical drop (fig. 136.), accompanied by a strong current. If glow be
produced, the drop will be smooth on the surface. If a short low brush is
formed, a minute tremulous motion of the liquid will be visible; but both
effects coincide with the principal one to be observed, namely, the regular
and successive charge of air, the formation of a wind or current, and the
form given by that current to the fluid drop, if a discharge ball be
gradually brought toward the cone, sparks will at last pass, and these will
be from the apex of the cone to the approached ball, indicating a
considerable degree of conducting power in this fluid.
1584. With a drop of water, the effects were of the same kind, and were
best obtained when a portion of gum water or of syrup hung from a ball
(fig. 137.). When the machine was worked slowly, a fine large quiet conical
drop, with concave lateral outline, and a small rounded end, was produced,
on which the glow appeared, whilst a steady wind issued, in a direction
from the point of the cone, of sufficient force to depress the surface of
uninsulated water held opposite to the termination. When the machine was
worked more rapidly some of the water was driven off; the smaller pointed
portion left was roughish on the surface, and the sound of successive brush
discharges was heard. With still more electricity, more water was
dispersed; that which remained was elongated and contracted, with an
alternating motion; a stronger brush discharge was heard, and the
vibrations of the water and the successive discharges of the individual
brushes were simultaneous. When water from beneath was brought towards the
drop, it did not indicate the same regular strong contracted current of air
as before; and when the distance was such that sparks passed, the water
beneath was _attracted_ rather than driven away, and the current of air
_ceased_.
1585. When the discharging ball was brought near the drop in its first
quiet glowing state (1582.), it converted that glow into brushes, and
caused the vibrating motion of the drop. When still nearer, sparks passed,
but they were always from the metal of the rod, over the surface of the
water, to the point, and then across the air to the ball. This is a natural
consequence of the deficient conducting power of the fluid (1584. 1585.).
1586. Why the drop vibrated, changing its form between the periods of
discharging brushes, so as to be more or less acute at particular instants,
to be most acute when the brush issued forth, and to be isochronous in its
action, and how the quiet glowing liquid drop, on assuming the conical
form, facilitated, as it were, the first action, are points, as to theory,
so evident, that I will not stop to speak of them. The principal thing to
observe at present is, the formation of the carrying current of air, and
the manner in which it exhibits its existence and influence by giving form
to the drop.
1587. That the drop, when of water, or a better conductor than water, is
formed into a cone principally by the current of air, is shown amongst
other ways (1594.) thus. A sharp point being held opposite the conical
drop, the latter soon lost its pointed form; was retraced and became round;
the current of air from it ceased, and was replaced by one from the point
beneath, which, if the latter were held near enough to the drop, actually
blew it aside, and rendered it concave in form.
1588. It is hardly necessary to say what happened with still worse
conductors than water, as oil, or oil of turpentine; the fluid itself was
then spun out into threads and carried off, not only because the air
rushing over its surface helped to sweep it away, but also because its
insulating particles assumed the same charged state as the particles of
air, and, not being able to discharge to them in a much greater decree than
the air particles themselves could do, were carried off by the same causes
which urged those in their course. A similar effect with melted sealing-wax
on a metal point forms an old and well-known experiment.
1589. A drop of gum water in the exhausted receiver of the air-pump was not
sensibly affected in its form when electrified. When air was let in, it
begun to show change of shape when the pressure was ten inches of mercury.
At the pressure of fourteen or fifteen inches the change was more sensible,
and as the air increased in density the effects increased, until they were
the same as those in the open atmosphere. The diminished effect in the rare
air I refer to the relative diminished energy of its current; that
diminution depending, in the first place, on the lower electric condition
of the electrified ball in the rarefied medium, and in the next, on the
attenuated condition of the dielectric, the cohesive force of water in
relation to rarefied air being something like that of mercury to dense air
(1581.), whilst that of water in dense air may be compared to that of
mercury in oil of turpentine (1597.).
1590. When a ball is covered with a thick conducting fluid, as treacle or
syrup, it is easy by inductive action to determine the wind from almost any
part of it (1577.); the experiment, which before was of rather difficult
performance, being rendered facile in consequence of the fluid enabling
that part, which at first was feeble in its action, to rise into an exalted
condition by assuming a pointed form.
1591. To produce the current, the electric intensity must rise and continue
at _one spot_, namely, at the origin of the current, higher than elsewhere,
and then, air having a uniform and ready access, the current is produced.
If no current be allowed (1574.), then discharge may take place by brush or
spark. But whether it be by brush or spark, or wind, it seems very probable
that the initial intensity or tension at which a particle of a given
gaseous dielectric charges, or commences discharge, is, under the
conditions before expressed, always the same (1410.).
1592. It is not supposed that all the air which enters into motion is
electrified; on the contrary, much that is not charged is carried on into
the stream. The part which is really charged may be but a small proportion
of that which is ultimately set in motion (1442.).
1593. When a drop of gum water (1584.) is made _negative_, it presents a
larger cone than when made positive; less of the fluid is thrown off, and
yet, when a ball is approached, sparks can hardly be obtained, so pointed
is the cone, and so free the discharge. A point held opposite to it did not
cause the retraction of the cone to such an extent as when it was positive.
All the effects are so different from those presented by the positive cone,
that I have no doubt such drops would present a very instructive method of
investigating the difference of positive and negative discharge in air and
other dielectrics (1480. 1501.).
1594. That I may not be misunderstood (1587.), I must observe here that I
do not consider the cones produced as the result _only_ of the current of
air or other insulating dielectric over their surface. When the drop is of
badly conducting matter, a part of the effect is due to the electrified
state of the particles, and this part constitutes almost the whole when the
matter is melted sealing-wax, oil of turpentine, and similar insulating
bodies (1588.). But even when the drop is of good conducting matter, as
water, solutions, or mercury, though the effect above spoken of will then
be insensible (1607.), still it is not the mere current of air or other
dielectric which produces all the change of form; for a part is due to
those attractive forces by which the charged drop, if free to move, would
travel along the line of strongest induction, and not being free to move,
has its form elongated until the _sum_ of the different forces tending to
produce this form is balanced by the cohesive attraction of the fluid. The
effect of the attractive forces are well shown when treacle, gum water, or
syrup is used; for the long threads which spin out, at the same time that
they form the axes of the currents of air, which may still be considered as
determined at their points, are like flexible conductors, and show by their
directions in what way the attractive forces draw them.
1595. When the phenomena of currents are observed in dense insulating
dielectrics, they present us with extraordinary degrees of mechanical
force. Thus, if a pint of well-rectified and filtered (1571.) oil of
turpentine be put into a glass vessel, and two wires be dipped into it in
different places, one leading to the electrical machine, and the other to
the discharging train, on working the machine the fluid will be thrown into
violent motion throughout its whole mass, whilst at the same time it will
rise two, three or four inches up the machine wire, and dart off jets from
it into the air.
1596. If very clean uninsulated mercury be at the bottom of the fluid, and
the wire from the machine be terminated either by a ball or a point, and
also pass through a glass tube extending both above and below the surface
of the oil of turpentine, the currents can be better observed, and will be
seen to rush down the wire, proceeding directly from it towards the
mercury, and there, diverging in all directions, will ripple its surface
strongly, and mounting up at the sides of the vessel, will return to
re-enter upon their course.
1597. A drop of mercury being suspended from an amalgamated brass ball,
preserved its form almost unchanged in air (1581.); but when immersed in
the oil of turpentine it became very pointed, and even particles of the
metal could be spun out and carried off by the currents of the dielectric.
The form of the liquid metal was just like that of the syrup in air
(1584.), the point of the cone being quite as fine, though not so long. By
bringing a sharp uninsulated point towards it, it could also be effected in
the same manner as the syrup drop in air (1587.), though not so readily,
because of the density and limited quantity of the dielectric.
1598. If the mercury at the bottom of the fluid be connected with the
electrical machine, whilst a rod is held in the hand terminating in a ball
three quarters of an inch, less or more, in diameter, and the ball be
dipped into the electrified fluid, very striking appearances ensue. When
the ball is raised again so as to be at a level nearly out of the fluid,
large portions of the latter will seem to cling to it (fig. 138.). If it be
raised higher, a column of the oil of turpentine will still connect it with
that in the basin below (fig. 139.). If the machine be excited into more
powerful action, this will become more bulky, and may then also be raised
higher, assuming the form (fig. 140); and all the time that these effects
continue, currents and counter-currents, sometimes running very close
together, may be observed in the raised column of fluid.
1599. It is very difficult to decide by sight the direction of the currents
in such experiments as these. If particles of silk are introduced they
cling about the conductors; but using drops of water and mercury the course
of the fluid dielectric seems well indicated. Thus, if a drop of water be
placed at the end of a rod (1571.) over the uninsulated mercury, it is soon
swept away in particles streaming downwards towards the mercury. If another
drop be placed on the mercury beneath the end of the rod, it is quickly
dispersed in all directions in the form of streaming particles, the
attractive forces drawing it into elongated portions, and the currents
carrying them away. If a drop of mercury be hung from a ball used to raise
a column of the fluid (1598.), then the shape of the drop seems to show
currents travelling in the fluid in the direction indicated by the arrows
(fig. 141.).
1600. A very remarkable effect is produced on these phenomena, connected
with positive and negative charge and discharge, namely, that a ball
charged positively raises a much higher and larger column of the oil of
turpentine than when charged negatively. There can be no doubt that this is
connected with the difference of positive and negative action already
spoken of (1480. 1525.), and tends much to strengthen the idea that such
difference is referable to the particles of the dielectric rather than to
the charged conductors, and is dependent upon the mode in which these
particles polarize (1503. 1523.).
1601. Whenever currents travel in insulating dielectrics they really effect
discharge; and it is important to observe, though a very natural result,
that it is indifferent which way the current or particles travel, as with
reversed direction their state is reversed. The change is easily made,
either in air or oil of turpentine, between two opposed rods, for an
insulated ball being placed in connexion with either rod and brought near
its extremity, will cause the current to set towards it from the opposite
end.
1602. The two currents often occur at once, as when both terminations
present brushes, and frequently when they exhibit the glow (1531.). In such
cases, the charged particles, or many of them, meet and mutually discharge
each other (1518. 1612.). If a smoking wax taper be held at the end of an
insulating rod towards a charged prime conductor, it will very often happen
that two currents will form, and be rendered visible by its vapour, one
passing as a fine filament of smoky particles directly to the charged
conductor, and the other passing as directly from the same taper wick
outwards, and from the conductor: the principles of inductric action and
charge, which were referred to in considering the relation of a carrier
ball and a conductor (1566.), being here also called into play.
* * * * *
1603. The general analogy and, I think I may say, identity of action found
to exist as to insulation and conduction (1338. 1561.) when bodies, the
best and the worst in the classes of insulators or conductors, were
compared, led me to believe that the phenomena of _convection_ in badly
conducting media were not without their parallel amongst the best
conductors, such even as the metals. Upon consideration, the cones produced
by Davy[A] in fluid metals, as mercury and tin, seemed to be cases in
point, and probably also the elongation of the metallic medium through
which a current of electricity was passing, described by Ampère (1113)[B];
for it is not difficult to conceive, that the diminution of convective
effect, consequent upon the high conducting power of the metallic media
used in these experiments, might be fully compensated for by the enormous
quantity of electricity passing. In fact, it is impossible not to expect
_some_ effect, whether sensible or not, of the kind in question, when such
a current is passing through a fluid offering a sensible resistance to the
passage of the electricity, and, thereby, giving proof of a certain degree
of insulating power (1328.).
[A] Philosophical Transactions, 1823, p. 155.
[B] Bibliothèque Universelle, xxi, 417.
1604. I endeavoured to connect the convective currents in air, oil of
turpentine, &c. and those in metals, by intermediate cases, but found this
not easy to do. On taking bodies, for instance, which, like water, adds,
solutions, fused salts or chlorides, &c., have intermediate conducting
powers, the minute quantity of electricity which the common machine can
supply (371. 861.) is exhausted instantly, so that the cause of the
phenomenon is kept either very low in intensity, or the instant of time
during which the effect lasts is so small, that one cannot hope to observe
the result sought for. If a voltaic battery be used, these bodies are all
electrolytes, and the evolution of gas, or the production of other changes,
interferes and prevents observation of the effect required.
1605. There are, nevertheless, some experiments which illustrate the
connection. Two platina wires, forming the electrodes of a powerful voltaic
battery, were placed side by side, near each other, in distilled water,
hermetically sealed up in a strong glass tube, some minute vegetable fibres
being present in the water. When, from the evolution of gas and the
consequent increased pressure, the bubbles formed on the electrodes were so
small as to produce but feebly ascending currents, then it could be
observed that the filaments present were attracted and repelled between the
two wires, as they would have been between two oppositely charged surfaces
in air or oil of turpentine, moving so quickly as to displace and disturb
the bubbles and the currents which these tended to form. Now I think it
cannot be doubted, that under similar circumstances, and with an abundant
supply of electricity, of sufficient tension also, convective currents
might have been formed; the attractions and repulsions of the filaments
were, in fact, the elements of such currents (1572.), and therefore water,
though almost infinitely above air or oil of turpentine as a conductor, is
a medium in which similar currents can take place.
1606. I had an apparatus made (fig. 142.) in which _a_ is a plate of
shell-lac, _b_ a fine platina wire passing through it, and having only the
section of the wire exposed above; _c_ a ring of bibulous paper resting on
the shell-lac, and _d_ distilled water retained by the paper in its place,
and just sufficient in quantity to cover the end of the wire _b_; another
wire, _e_, touched a piece of tinfoil lying in the water, and was also
connected with a discharging train; in this way it was easy, by rendering
_b_ either positive or negative, to send a current of electricity by its
extremity into the fluid, and so away by the wire _e_.
1607. On connecting _b_ with the conductor of a powerful electrical
machine, not the least disturbance of the level of the fluid over the end
of the wire during the working of the machine could be observed; but at the
same time there was not the smallest indication of electrical charge about
the conductor of the machine, so complete was the discharge. I conclude
that the quantity of electricity passed in a _given time_ had been too
small, when compared with the conducting power of the fluid to produce the
desired effect.
1608. I then charged a large Leyden battery (291.), and discharged it
through the wire _b_, interposing, however, a wet thread, two feet long, to
prevent a spark in the water, and to reduce what would else have been a
sudden violent discharge into one of more moderate character, enduring for
a sensible length of time (334.). I now did obtain a very brief elevation
of the water over the end of the wire; and though a few minute bubbles of
gas were at the same time formed there, so as to prevent me from asserting
that the effect was unequivocally the same as that obtained by DAVY in the
metals, yet, according to my best judgement, it was partly, and I believe
principally, of that nature.
1609. I employed a voltaic battery of 100 pair of four-inch plates for
experiments of a similar nature with electrolytes. In these cases the
shell-lac was cupped, and the wire _b_ 0.2 of an inch in diameter.
Sometimes I used a positive amalgamated zinc wire in contact with dilute
sulphuric acid; at others, a negative copper wire in a solution of sulphate
of copper; but, because of the evolution of gas, the precipitation of
copper, &c., I was not able to obtain decided results. It is but right to
mention, that when I made use of mercury, endeavouring to repeat DAVY's
experiment, the battery of 100 pair was not sufficient to produce the
elevations[A].
[A] In the experiments at the Royal Institution, Sir H. Davy used, I
think, 500 or 600 pairs of plates. Those at the London Institution
were made with the apparatus of Mr. Pepys (consisting of an enormous
single pair of plates), described in the Philosophical Transactions
for 1832, p. 187.
1610. The latter experiments (1609.) may therefore be considered as failing
to give the hoped-for proof, but I have much confidence in the former
(1605. 1608.), and in the considerations (1603.) connected with them. If I
have rightly viewed them, and we may be allowed to compare the currents at
points and surfaces in such extremely different bodies as air and the
metals, and admit that they are effects of the _same_ kind, differing only
in degree and in proportion to the insulating or conducting power of the
dielectric used, what great additional argument we obtain in favour of that
theory, which in the phenomena of insulation and conduction also, as in
these, would link _the same_ apparently dissimilar substances together
(1336. 1561.); and how completely the general view, which refers all the
phenomena to the direct action of the molecules of matter, seems to embrace
the various isolated phenomena as they successively come under
consideration!
* * * * *
1611. The connection of this convective or carrying effect, which depends
upon a certain degree of insulation, with conduction; i.e. the occurrence
of both in so many of the substances referred to, as, for instance, the
metals, water, air, &c., would lead to many very curious theoretical
generalizations, which I must not indulge in here. One point, however, I
shall venture to refer to. Conduction appears to be essentially an action
of contiguous particles, and the considerations just stated, together with
others formerly expressed (1326, 1336, &c.), lead to the conclusion, that
all bodies conduct, and by the same process, air as well as metals; the
only difference being in the necessary degree of force or tension between
the particles which must exist before the act of conduction or transfer
from one particle to another can take place.
1612. The question then arises, what is this limiting condition which
separates, as it were, conduction and insulation from each other? Does it
consist in a difference between the two contiguous particles, or the
contiguous poles of these particles, in the nature and amount of positive
and negative force, no communication or discharge occurring unless that
difference rises up to a certain degree, variable for different bodies, but
always the same for the same body? Or is it true that, however small the
difference between two such particles, if _time_ be allowed, equalization
of force will take place, even with the particles of such bodies as air,
sulphur or lac? In the first case, insulating power in any particular body
would be proportionate to the degree of the assumed necessary difference of
force; in the second, to the _time_ required to equalize equal degrees of
difference in different bodies. With regard to airs, one is almost led to
expect a permanent difference of force; but in all other bodies, time seems
to be quite sufficient to ensure, ultimately, complete conduction. The
difference in the modes by which insulation may be sustained, or conduction
effected, is not a mere fanciful point, but one of great importance, as
being essentially connected with the molecular theory of induction, and the
manner in which the particles of bodies assume and retain their polarized
state.
* * * * *
¶ xi. _Relation of a vacuum to electrical phenomena._
1613. It would seem strange, if a theory which refers all the phenomena of
insulation and conduction, i.e. all electrical phenomena, to the action of
contiguous particles, were to omit to notice the assumed possible case of a
_vacuum_. Admitting that a vacuum can be produced, it would be a very
curious matter indeed to know what its relation to electrical phenomena
would be; and as shell-lac and metal are directly opposed to each other,
whether a vacuum would be opposed to them both, and allow neither of
induction or conduction across it. Mr. Morgan[A] has said that a vacuum
does not conduct. Sir H. Davy concluded from his investigations, that as
perfect a vacuum as could be made[B] did conduct, but does not consider the
prepared spaces which he used as absolute vacua. In such experiments I
think I have observed the luminous discharge to be principally on the inner
surface of the glass; and it does not appear at all unlikely, that, if the
vacuum refused to conduct, still the surface of glass next it might carry
on that action.
[A] Philosophical Transactions, 1785, p. 272
[B] Ibid. 1822, p. 64.
1614. At one time, when I thought inductive force was exerted in right
lines, I hoped to illustrate this important question by making experiments
on induction with metallic mirrors (used only as conducting vessels)
exposed towards a very clear sky at night time, and of such concavity that
nothing but the firmament could be visible from the lowest part of the
concave _n_, fig. 143. Such mirrors, when electrified, as by connexion with
a Leyden jar, and examined by a carrier ball, readily gave electricity at
the lowest part of their concavity if in a room; but I was in hopes of
finding that, circumstanced as before stated, they would give little or
none at the same spot, if the atmosphere above really terminated in a
vacuum. I was disappointed in the conclusion, for I obtained as much
electricity there as before; but on discovering the action of induction in
curved lines (1231.), found a full and satisfactory explanation of the
result.
1615. My theory, as far as I have ventured it, does not pretend to decide
upon the consequences of a vacuum. It is not at present limited
sufficiently, or rendered precise enough, either by experiments relating to
spaces void of matter, or those of other kinds, to indicate what would
happen in the vacuum case. I have only as yet endeavoured to establish,
what all the facts seem to prove, that when electrical phenomena, as those
of induction, conduction, insulation and discharge occur, they depend on,
and are produced by the action of _contiguous_ particles of matter, the
next existing particle being considered as the contiguous one; and I have
further assumed, that these particles are polarized; that each exhibits the
two forces, or the force in two directions (1295. 1298.); and that they act
at a distance, only by acting on the _contiguous_ and intermediate
particles.
1616. But assuming that a perfect vacuum were to intervene in the course of
the lines of inductive action (1304.), it does not follow from this theory,
that the particles on opposite sides of such a vacuum could not act on each
other. Suppose it possible for a positively electrified particle to be in
the centre of a vacuum an inch in diameter, nothing in my present views
forbids that the particle should act at the distance of half an inch on all
the particles forming the inner superficies of the bounding sphere, and
with a force consistent with the well-known law of the squares of the
distance. But suppose the sphere of an inch were full of insulating matter,
the electrified particle would not then, according to my notion, act
directly on the distant particles, but on those in immediate association
with it, employing _all_ its power in polarizing them; producing in them
negative force equal in amount to its own positive force and directed
towards the latter, and positive force of equal amount directed outwards
and acting in the same manner upon the layer of particles next in
succession. So that ultimately, those particles in the surface of a sphere
of half an inch radius, which were acted on _directly_ when that sphere was
a vacuum, will now be acted on _indirectly_ as respects the central
particle or source of action, i.e. they will be polarized in the same way,
and with the same amount of force.
§ 19. _Nature of the electric current._
1617. The word _current_ is so expressive in common language, that when
applied in the consideration of electrical phenomena we can hardly divest
it sufficiently of its meaning, or prevent our minds from being prejudiced
by it (283. 511.). I shall use it in its common electrical sense, namely,
to express generally a certain condition and relation of electrical forces
supposed to be in progression.
1618. A current is produced both by excitement and discharge; and
whatsoever the variation of the two general causes may be, the effect
remains the same. Thus excitement may occur in many ways, as by friction,
chemical action, influence of heat, change of condition, induction, &c.;
and discharge has the forms of conduction, electrolyzation, disruptive
discharge, and convection; yet the current connected with these actions,
when it occurs, appears in all cases to be the same. This constancy in the
character of the current, notwithstanding the particular and great
variations which may be made in the mode of its occurrence, is exceedingly
striking and important; and its investigation and development promise to
supply the most open and advantageous road to a true and intimate
understanding of the nature of electrical forces.
1619. As yet the phenomena of the current have presented nothing in
opposition to the view I have taken of the nature of induction as an action
of contiguous particles. I have endeavoured to divest myself of prejudices
and to look for contradictions, but I have not perceived any in conductive,
electrolytic, convective, or disruptive discharge.
1620. Looking at the current as a _cause_, it exerts very extraordinary and
diverse powers, not only in its course and on the bodies in which it
exists, but collaterally, as in inductive or magnetic phenomena.
1621. _Electrolytic action._--One of its direct actions is the exertion of
pure chemical force, this being a result which has now been examined to a
considerable extent. The effect is found to be _constant_ and _definite_
for the quantity of electric force discharged (783. &c.); and beyond that,
the _intensity_ required is in relation to the intensity of the affinity or
forces to be overcome (904. 906. 911.). The current and its consequences
are here proportionate; the one may be employed to represent the other; no
part of the effect of either is lost or gained; so that the case is a
strict one, and yet it is the very case which most strikingly illustrates
the doctrine that induction is an action of contiguous particles (1164.
1343.).
1622. The process of electrolytic discharge appears to me to be in close
analogy, and perhaps in its nature identical with another process of
discharge, which at first seems very different from it, I mean _convection_
(1347. 1572.). In the latter case the particles may travel for yards across
a chamber; they may produce strong winds in the air, so as to move
machinery; and in fluids, as oil of turpentine, may even shake the hand,
and carry heavy metallic bodies about[A]; and yet I do not see that the
force, either in kind or action, is at all different to that by which a
particle of hydrogen leaves one particle of oxygen to go to another, or by
which a particle of oxygen travels in the contrary direction.
[A] If a metallic vessel three or four inches deep, containing oil of
turpentine, be insulated and electrified, and a rod with a ball (an
inch or more in diameter) at the end have the ball immersed in the
fluid whilst the end is held in the hand, the mechanical force
generated when the ball is moved to and from the sides of the vessel
will soon be evident to the experimenter.
1623. Travelling particles of the air can effect chemical changes just as
well as the contact of a fixed platina electrode, or that of a combining
electrode, or the ions of a decomposing electrolyte (453. 471.); and in the
experiment formerly described, where eight places of decomposition were
rendered active by one current (469.), and where charged particles of air
in motion were the only electrical means of connecting these parts of the
current, it seems to me that the action of the particles of the electrolyte
and of the air were essentially the same. A particle of air was rendered
positive; it travelled in a certain determinate direction, and coming to an
electrolyte, communicated its powers; an equal amount of positive force was
accordingly acquired by another particle (the hydrogen), and the latter, so
charged, travelled as the former did, and in the same direction, until it
came to another particle, and transferred its power and motion, making that
other particle active. Now, though the particle of air travelled over a
visible and occasionally a large space, whilst the particle of the
electrolyte moved over an exceedingly small one; though the air particle
might be oxygen, nitrogen, or hydrogen, receiving its charge from force of
high intensity, whilst the electrolytic particle of hydrogen had a natural
aptness to receive the positive condition with extreme facility; though the
air particle might be charged with very little electricity at a very high
intensity by one process, whilst the hydrogen particle might be charged
with much electricity at a very low intensity by another process; these are
not differences of kind, as relates to the final discharging action of
these particles, but only of degree; not essential differences which make
things unlike, but such differences as give to things, similar in their
nature, that great variety which fits them for their office in the system
of the universe.
1624. So when a particle of air, or of dust in it, electrified at a
negative point, moves on through the influence of the inductive forces
(1572.) to the next positive surface, and after discharge passes away, it
seems to me to represent exactly that particle of oxygen which, having been
rendered negative in the electrolyte, is urged by the same disposition of
inductive forces, and going to the positive platina electrode, is there
discharged, and then passes away, as the air or dust did before it.
1625. _Heat_ is another direct effect of the _current_ upon substances in
which it occurs, and it becomes a very important question, as to the
relation of the electric and heating forces, whether the latter is always
definite in amount[A]. There are many cases, even amongst bodies which
conduct without change, that at present are irreconcileable with the
assumption that it is[B]; but there are also many which indicate that, when
proper limitations are applied, the heat produced is definite. Harris has
shown this for a given length of current in a metallic wire, using common
electricity[C]; and De la Rive has proved the same point for voltaic
electricity by his beautiful application of Breguet's thermometer[D].
[A] See De la Rive's Researches, Bib. Universelle, 1829, xl. p. 40.
[B] Amongst others, Davy, Philosophical Transactions, 1821, p. 438.
Pelletier's important results, Annales de Chimie, 1834, lvi. p. 371.
and Becquerel's non-heating current, Bib. Universelle, 1835, lx. 218.
[C] Philosophical Transactions, 1824, pp. 225. 228.
[D] Annales de Chimie, 1836, lxii. 177.
1626. When the production of heat is observed in electrolytes under
decomposition, the results are still more complicated. But important steps
have been taken in the investigation of this branch of the subject by De la
Rive[A] and others; and it is more than probable that, when the right
limitations are applied, constant and definite results will here also be
obtained.
[A] Bib. Universelle, 1829, xl. 49; and Ritchie, Phil. Trans. 1832. p.
296.
* * * * *
1627. It is a most important part of the character of the current, and
essentially connected with its very nature, that it is always the same. The
two forces are everywhere in it. There is never one current of force or one
fluid only. Any one part of the current may, as respects the presence of
the two forces there, be considered as precisely the same with any other
part; and the numerous experiments which imply their possible separation,
as well as the theoretical expressions which, being used daily, assume it,
are, I think, in contradiction with facts (511, &c.). It appears to me to
be as impossible to assume a current of positive or a current of negative
force alone, or of the two at once with any predominance of one over the
other, as it is to give an absolute charge to matter (516. 1169. 1177.).
1628. The establishment of this truth, if, as I think, it be a truth, or on
the other hand the disproof of it, is of the greatest consequence. If, as a
first principle, we can establish, that the centres of the two forces, or
elements of force, never can be separated to any sensible distance, or at
all events not further than the space between two contiguous particles
(1615.), or if we can establish the contrary conclusion, how much more
clear is our view of what lies before us, and how much less embarrassed the
ground over which we have to pass in attaining to it, than if we remain
halting between two opinions! And if, with that feeling, we rigidly test
every experiment which bears upon the point, as far as our prejudices will
let us (1161.), instead of permitting them with a theoretical expression to
pass too easily away, are we not much more likely to attain the real truth,
and from that proceed with safety to what is at present unknown?
1629. I say these things, not, I hope, to advance a particular view, but to
draw the strict attention of those who are able to investigate and judge of
the matter, to what must be a turning point in the theory of electricity;
to a separation of two roads, one only of which can be right: and I hope I
may be allowed to go a little further into the facts which have driven me
to the view I have just given.
1630. When a wire in the voltaic circuit is heated, the temperature
frequently rises first, or most at one end. If this effect were due to any
relation of positive or negative as respects the current, it would be
exceedingly important. I therefore examined several such cases; but when,
keeping the contacts of the wire and its position to neighbouring things
unchanged, I altered the direction of the current, I found that the effect
remained unaltered, showing that it depended, not upon the direction of the
current, but on other circumstances. So there is here no evidence of a
difference between one part of the circuit and another.
1631. The same point, i.e. uniformity in every part, may be illustrated by
what may be considered as the inexhaustible nature of the current when
producing particular effects; for these effects depend upon transfer only,
and do not consume the power. Thus a current which will heat one inch of
platina wire will heat a hundred inches (853. note). If a current be
sustained in a constant state, it will decompose the fluid in one
voltameter only, or in twenty others if they be placed in the circuit, in
each to an amount equal to that in the single one.
1632. Again, in cases of disruptive discharge, as in the spark, there is
frequently a dark part (1422.) which, by Professor Johnson, has been called
the neutral point[A]; and this has given rise to the use of expressions
implying that there are two electricities existing separately, which,
passing to that spot, there combine and neutralize each other[B]. But if
such expressions are understood as correctly indicating that positive
electricity alone is moving between the positive ball and that spot, and
negative electricity only between the negative ball and that spot, then
what strange conditions these parts must be in; conditions, which to my
mind are every way unlike those which really occur! In such a case, one
part of a current would consist of positive electricity only, and that
moving in one direction; another part would consist of negative electricity
only, and that moving in the other direction; and a third part would
consist of an accumulation of the two electricities, not moving in either
direction, but mixing up together! and being in a relation to each other
utterly unlike any relation which could be supposed to exist in the two
former portions of the discharge. This does not seem to me to be natural.
In a current, whatever form the discharge may take, or whatever part of the
circuit or current is referred to, as much positive force as is there
exerted in one direction, so much negative force is there exerted in the
other. If it were not so we should have bodies electrified not merely
positive and negative, but on occasions in a most extraordinary manner, one
being charged with five, ten, or twenty times as much of both positive and
negative electricity in equal quantities as another. At present, however,
there is no known fact indicating such states.
[A] Silliman's Journal, 1834, xxv. p. 57.
[B] Thomson on Heat and Electricity, p. 171.
1633. Even in cases of convection, or carrying discharge, the statement
that the current is everywhere the same must in effect be true (1627.); for
how, otherwise, could the results formerly described occur? When currents
of air constituted the mode of discharge between the portions of paper
moistened with iodide of potassium or sulphate of soda (465. 469.),
decomposition occurred; and I have since ascertained that, whether a
current of positive air issued from a spot, or one of negative air passed
towards it, the effect of the evolution of iodine or of acid was the same,
whilst the reversed currents produced alkali. So also in the magnetic
experiments (307.) whether the discharge was effected by the introduction
of a wire, or the occurrence of a spark, or the passage of convective
currents either one way or the other (depending on the electrified state of
the particles), the result was the same, being in all cases dependent upon
the perfect current.
1634. Hence, the section of a current compared with other sections of the
same current must be a constant quantity, if the actions exerted be of the
same kind; or if of different kinds, then the forms under which the effects
are produced are equivalent to each other, and experimentally convertible
at pleasure. It is in sections, therefore, we must look for identity of
electrical force, even to the sections of sparks and carrying actions, as
well as those of wires and electrolytes.
1635. In illustration of the utility and importance of establishing that
which may be the true principle, I will refer to a few cases. The doctrine
of unipolarity, as formerly stated, and I think generally understood[A], is
evidently inconsistent with my view of a current (1627.); and the later
singular phenomena of poles and flames described by Erman and others[B]
partake of the same inconsistency of character. If a unipolar body could
exist, i.e. one that could conduct the one electricity and not the other,
what very new characters we should have a right to expect in the currents
of single electricities passing through them, and how greatly ought they to
differ, not only from the common current which is supposed to have both
electricities travelling in opposite directions in equal amount at the same
time, but also from each other! The facts, which are excellent, have,
however, gradually been more correctly explained by Becquerel[C],
Andrews[D], and others; and I understand that Professor Ohms[E] has
perfected the work, in his close examination of all the phenomena; and
after showing that similar phenomena can take place with good conductors,
proves that with soap, &c. many of the effects are the mere consequences of
the bodies evolved by electrolytic action.
[A] Erman, Annales de Chimie, 1807. lxi. p. 115. Davy's Elements, p.
168. Biot, Ency. Brit. Supp, iv. p. 444. Becquerel, Traité, i. p. 167.
De la Rive, Bib. Univ. 1837. vii. 392.
[B] Erman, Annales de Chimie, 1824. xxv. 278. Becquerel, Ibid. xxxvi.
p. 329
[C] Becquerel, Annales de Chimie, 1831. xlvi. p. 283.
[D] Andrews, Philosophical Magazine, 1836. ix. 182.
[E] Schweigger's Jahrbuch de Chimie, &c. 1830. Heft 8. Not
understanding German, it is with extreme regret I confess I have not
access, and cannot do justice, to the many most valuable papers in
experimental electricity published in that language. I take this
opportunity also of stating another circumstance which occasions me
great trouble, and, as I find by experience, may make, me seemingly
regardless of the labours of others:--it is a gradual loss of memory
for some years past; and now, often when I read a memoir, I remember
that I have seen it before, and would have rejoiced if at the right
time I could have recollected and referred to it in the progress of my
own papers.--M.F.
1636. I conclude, therefore, that the _facts_ upon which the doctrine of
unipolarity was founded are not adverse to that unity and indivisibility of
character which I have stated the current to possess, any more than the
phenomena of the pile itself (which might well bear comparison with those
of unipolar bodies,) are opposed to it. Probably the effects which have
been called effects of unipolarity, and the peculiar differences of the
positive and negative surface when discharging into air, gases, or other
dielectrics (1480. 1525.) which have been already referred to, may have
considerable relation to each other[A].
[A] See also Hare in Silliman's Journal, 1833. xxiv. 246.
* * * * *
1637. M. de la Rive has recently described a peculiar and remarkable effect
of heat on a current when passing between electrodes and a fluid[A]. It is,
that if platina electrodes dip into acidulated water, no change is produced
in the passing current by making the positive electrode hotter or colder;
whereas making the negative electrode hotter increased the deflexion of a
galvanometer affected by the current, from 12° to 30° and even 45°, whilst
making it colder diminished the current in the same high proportions.
[A] Bibliothèque Universelle, 1837, vii. 388.
1638. That one electrode should have this striking relation to heat whilst
the other remained absolutely without, seem to me as incompatible with what
I conceived to be the character of a current as unipolarity (1627. 1635.),
and it was therefore with some anxiety that I repeated the experiment. The
electrodes which I used were platina; the electrolyte, water containing
about one sixth of sulphuric acid by weight: the voltaic battery consisted
of two pairs of amalgamated zinc and platina plates in dilute sulphuric
acid, and the galvanometer in the circuit was one with two needles, and
gave when the arrangement was complete a deflexion of 10° or 12°.
1639. Under these circumstances heating either electrode increased the
current; heating both produced still more effect. When both were heated, if
either were cooled, the effect on the current fell in proportion. The
proportion of effect due to heating this or that electrode varied, but on
the whole heating the negative seemed to favour the passage of the current
somewhat more than heating the positive. Whether the application of heat
were by a flame applied underneath, or one directed by a blowpipe from
above, or by a hot iron or coal, the effect was the same.
1640. Having thus removed the difficulty out of the way of my views
regarding a current, I did not pursue this curious experiment further. It
is probable, that the difference between my results and those of M. de la
Rive may depend upon the relative values of the currents used; for I
employed only a weak one resulting from two pairs of plates two inches long
and half an inch wide, whilst M. de la Rive used four pairs of plates of
sixteen square inches in surface.
* * * * *
1641. Electric discharges in the atmosphere in the form of balls of fire
have occasionally been described. Such phenomena appear to me to be
incompatible with all that we know of electricity and its modes of
discharge. As _time_ is an element in the effect (1418. 1436.) it is
possible perhaps that an electric discharge might really pass as a ball
from place to place; but as every thing shows that its velocity must be
almost infinite, and the time of its duration exceedingly small, it is
impossible that the eye should perceive it as anything else than a line of
light. That phenomena of balls of fire may appear in the atmosphere, I do
not mean to deny; but that they have anything to do with the discharge of
ordinary electricity, or are at all related to lightning or atmospheric
electricity, is much more than doubtful.
* * * * *
1642. All these considerations, and many others, help to confirm the
conclusion, drawn over and over again, that the current is an indivisible
thing; an axis of power, in every part of which both electric forces are
present in equal amount[A] (517. 1627.). With conduction and
electrolyzation, and even discharge by spark, such a view will harmonize
without hurting any of our preconceived notions; but as relates to
convection, a more startling result appears, which must therefore be
considered.
[A] I am glad to refer here to the results obtained by Mr. Christie
with magneto-electricity, Philosophical Transactions, 1833, p. 113
note. As regards the current in a wire, they confirm everything that I
am contending for.
1643. If two balls A and B be electrified in opposite states and held
within each other's influence, the moment they move towards each other, a
current, or those effects which are understood by the word current, will be
produced. Whether A move towards B, or B move in the opposite direction
towards A, a current, and in both cases having the same _direction_, will
result. If A and B move from each other, then a _current_ in the opposite
direction, or equivalent effects, will be produced.
1644. Or, as charge exists only by induction (1178. 1299.), and a body when
electrified is necessarily in relation to other bodies in the opposite
state; so, if a ball be electrified positively in the middle of a room and
be then moved in any direction, effects will be produced, as _current_ in
the same direction (to use the conventional mode of expression) had
existed: or, if the ball be negatively electrified, and then moved, effects
as if a current in a direction contrary to that of the motion had been
formed, will be produced.
1645. I am saying of a single particle or of two what I have before said,
in effect, of many (1633.). If the former account of currents be true, then
that just stated must be a necessary result. And, though the statement may
seem startling at first, it is to be considered that, according to my
theory of induction, the charged conductor or particle is related to the
distant conductor in the opposite state, or that which terminates the
extent of the induction, by all the intermediate particles (1165, 1295.),
these becoming polarized exactly as the particles of a solid electrolyte do
when interposed between the two electrodes. Hence the conclusion regarding
the unity and identity of the current in the case of convection, jointly
with the former cases, is not so strange as it might at first appear.
* * * * *
1646. There is a very remarkable phenomenon or effect of the electrolytic
discharge, first pointed out, I believe, by Mr. Porrett, of the
accumulation of fluid under decomposing action in the current on one side
of an interposed diaphragm[A]. It is a mechanical result; and as the liquid
passes from the positive towards the negative electrode in all the known
cases, it seems to establish a relation to the polar condition of the
dielectric in which the current exists (1164. 1525.). It has not as yet
been sufficiently investigated by experiment; for De la Rive says[B], it
requires that the water should be a bad conductor, as, for instance,
distilled water, the effect not happening with strong solutions; whereas,
Dutrochet says[C] the contrary is the case, and that, the effect is not
directly due to the electric current.
[A] Annals of Philosophy, 1816. viii. p. 75.
[B] Annales de Chimie, 1835. xxviii. p. 196.
[C] Annales de Chimie, 1832, xlix. p. 423.
1647. Becquerel, in his Traité de l'Electricité, has brought together the
considerations which arise for and against the opinion, that the effect
generally is an electric effect[A]. Though I have no decisive fact to quote
at present, I cannot refrain from venturing an opinion, that the effect is
analogous both to combination and convection (1623.), being a case of
carrying due to the relation of the diaphragm and the fluid in contact with
it, through which the electric discharge is jointly effected; and further,
that the peculiar relation of positive and negative small and large
surfaces already referred to (1482. 1503. 1525.), may be the direct cause
of the fluid and the diaphragm travelling in contrary but determinate
directions. A very valuable experiment has been made by M. Becquerel with
particles of clay[B], which will probably bear importantly on this point.
[A] Vol. iv. p. 192, 197.
[B] Traité de l'Electricité, i. p. 285.
* * * * *
1648. _As long as_ the terms _current_ and _electro-dynamic_ are used to
express those relations of the electric forces in which progression of
either fluids or effects are supposed to occur (283.), _so long_ will the
idea of velocity be associated with them; and this will, perhaps, be more
especially the case if the hypothesis of a fluid or fluids be adopted.
1649. Hence has arisen the desire of estimating this velocity either
directly or by some effect dependent on it; and amongst the endeavours to
do this correctly, may be mentioned especially those of Dr. Watson[A] in
1748, and of Professor Wheatstone[B] in 1834; the electricity in the early
trials being supposed to travel from end to end of the arrangement, but in
the later investigations a distinction occasionally appearing to be made
between the transmission of the effect and of the supposed fluid by the
motion of whose particles that effect is produced.
[A] Philosophical Transactions, 1748.
[B] Ibid. 1834, p. 583.
1650. Electrolytic action has a remarkable bearing upon this question of
the velocity of the current, especially as connected with the theory of an
electric fluid or fluids. In it there is an evident transfer of power with
the transfer of each particle of the anion or cathion present, to the next
particles of the cathion or anion; and as the amount of power is definite,
we have in this way a means of localizing as it were the force, identifying
it by the particle and dealing it out in successive portions, which leads,
I think, to very striking results.
1651. Suppose, for instance, that water is undergoing decomposition by the
powers of a voltaic battery. Each particle of hydrogen as it moves one way,
or of oxygen as it moves in the other direction, will transfer a certain
amount of electrical force associated with it in the form of chemical
affinity (822. 852. 918.) onwards through a distance, which is equal to
that through which the particle itself has moved. This transfer will be
accompanied by a corresponding movement in the electrical forces throughout
every part of the circuit formed (1627. 1634.), and its effects may be
estimated, as, for instance, by the heating of a wire (853.) at any
particular section of the current however distant. If the water be a cube
of an inch in the side, the electrodes touching, each by a surface of one
square inch, and being an inch apart, then, by the time that a tenth of it,
or 25.25 grs., is decomposed, the particles of oxygen and hydrogen
throughout the mass may be considered as having moved relatively to each
other in opposite directions, to the amount of the tenth of an inch; i.e.
that two particles at first in combination will after the motion be the
tenth of an inch apart. Other motions which occur in the fluid will not at
all interfere with this result; for they have no power of accelerating or
retarding the electric discharge, and possess in fact no relation to it.
1652. The quantity of electricity in 25.25 grains of water is, according to
an estimate of the force which I formerly made (861.), equal to above 24
millions of charges of a large Leyden battery; or it would have kept any
length of a platina wire 1/104 of an inch in diameter red-hot for an hour
and a half (853.). This result, though given only as an approximation, I
have seen no reason as yet to alter, and it is confirmed generally by the
experiments and results of M. Pouillet[A]. According to Mr. Wheatstone's
experiments, the influence or effects of the current would appear at a
distance of 576,000 miles in a second[B]. We have, therefore, in this view
of the matter, on the one hand, an enormous quantity of power equal to a
most destructive thunder-storm appearing instantly at the distance of
576,000 miles from its source, and on the other, a quiet effect, in
producing which the power had taken an hour and a half to travel through
the tenth of an inch: yet these are the equivalents to each other, being
effects observed at the sections of one and the same current (1634.).
[A] Becquerel, Traité de l'Electricité, v. p. 278.
[B] Philosophical Transactions, 1834, p. 589.
* * * * *
1653. It is time that I should call attention to the lateral or transverse
forces of the _current_. The great things which have been achieved by
Oersted, Arago, Ampère, Davy, De la Rive, and others, and the high degree
of simplification which has been introduced into their arrangement by the
theory of Ampère, have not only done their full service in advancing most
rapidly this branch of knowledge, but have secured to it such attention
that there is no necessity for urging on its pursuit. I refer of course to
magnetic action and its relations; but though this is the only recognised
lateral action of the current, there is great reason for believing that
others exist and would by their discovery reward a close search for them
(951.).
1654. The magnetic or transverse action of the current seems to be in a
most extraordinary degree independent of those variations or modes of
action which it presents directly in its course; it consequently is of the
more value to us, as it gives us a higher relation of the power than any
that might have varied with each mode of discharge. This discharge, whether
it be by conduction through a wire with infinite velocity (1652.), or by
electrolyzation with its corresponding and exceeding slow motion (1651.),
or by spark, and probably even by convection, produces a transverse
magnetic action always the same in kind and direction.
1655. It has been shown by several experimenters, that whilst the discharge
is of the _same kind_ the amount of lateral or magnetic force is very
constant (216. 366. 367. 368. 376.). But when we wish to compare discharge
of different kinds, for the important purpose of ascertaining whether the
same amount of current will in its _different forms_ produce the same
amount of transverse action, we find the data very imperfect. Davy noticed,
that when the electric current was passing through an aqueous solution it
affected a magnetic needle[A], and Dr. Ritchie says, that the current in
the electrolyte is as magnetic as that in a metallic wire[B], and has
caused water to revolve round a magnet as a wire carrying the current would
revolve.
[A] Philosophical Transactions, 1821, p. 426.
[B] Ibid. 1832, p. 294.
1656. Disruptive discharge produces its magnetic effects: a strong spark,
passed transversely to a steel needle, will magnetise it as well as if the
electricity of the spark were conducted by a metallic wire occupying the
line of discharge; and Sir H. Davy has shown that the discharge of a
voltaic battery in vacuo is affected and has motion given to it by
approximated magnets[A].
[A] Philosophical Transactions, 1821, p. 427.
1657. Thus the three very different modes of discharge, namely, conduction,
electrolyzation, and disruptive discharge, agree in producing the important
transverse phenomenon of magnetism. Whether convection or carrying
discharge will produce the same phenomenon has not been determined, and the
few experiments I have as yet had time to make do not enable me to answer
in the affirmative.
* * * * *
1658. Having arrived at this point in the consideration of the current and
in the endeavour to apply its phenomena as tests of the truth or fallacy of
the theory of induction which I have ventured to set forth, I am now very
much tempted to indulge in a few speculations respecting its lateral action
and its possible connexion with the transverse condition of the lines of
ordinary induction (1165, 1304.)[A]. I have long sought and still seek for
an effect or condition which shall be to statical electricity what magnetic
force is to current electricity (1411.); for as the lines of discharge are
associated with a certain transverse effect, so it appeared to me
impossible but that the lines of tension or of inductive action, which of
necessity precede that discharge, should also have their correspondent
transverse condition or effect (951.).
[A] Refer for further investigations to 1709.--1736.--_Dec. 1838._
1659. According to the beautiful theory of Ampère, the transverse force of
a current may be represented by its attraction for a similar current and
its repulsion of a contrary current. May not then the equivalent transverse
force of static electricity be represented by that lateral tension or
repulsion which the lines of inductive action appear to possess (1304.)?
Then again, when current or discharge occurs between two bodies, previously
under inductrical relations to each other, the lines of inductive force
will weaken and fade away, and, as their lateral repulsive tension
diminishes, will contract and ultimately disappear in the line of
discharge. May not this be an effect identical with the attractions of
similar currents? i.e. may not the passage of static electricity into
current electricity, and that of the lateral tension of the lines of
inductive force into the lateral attraction of lines of similar discharge,
have the same relation and dependences, and run parallel to each other?
1660. The phenomena of induction amongst currents which I had the good
fortune to discover some years ago (6. &c. 1048.) may perchance here form a
connecting link in the series of effects. When a current is first formed,
it tends to produce a current in the contrary direction in all the matter
around it; and if that matter have conducting properties and be fitly
circumstanced, such a current is produced. On the contrary, when the
original current is stopped, one in the same direction tends to form all
around it, and, in conducting matter properly arranged, will be excited.
1661. Now though we perceive the effects only in that portion of matter
which, being in the neighbourhood, has conducting properties, yet
hypothetically it is probable, that the nonconducting matter has also its
relations to, and is affected by, the disturbing cause, though we have not
yet discovered them. Again and again the relation of conductors and
non-conductors has been shown to be one not of opposition in kind, but only
of degree (1334, 1603.); and, therefore, for this, as well as for other
reasons, it is probable, that what will affect a conductor will affect an
insulator also; producing perhaps what may deserve the term of the
electrotonic state (60. 242. 1114.).
1662. It is the feeling of the necessity of some lateral connexion between
the lines of electric force (1114.); of some link in the chain of effects
as yet unrecognised, that urges me to the expression of these speculations.
The same feeling has led me to make many experiments on the introduction of
insulating dielectrics having different inductive capacities (1270. 1277.)
between magnetic poles and wires carrying currents, so as to pass across
the lines of magnetic force. I have employed such bodies both at rest and
in motion, without, as yet, being able to detect any influence produced by
them; but I do by no means consider the experiments as sufficiently
delicate, and intend, very shortly, to render them more decisive[A].
[A] See onwards 1711.--1726.--_Dec. 1838._
1663. I think the hypothetical question may at present be put thus: can
such considerations as those already generally expressed (1658.) account
for the transverse effects of electrical currents? are two such currents in
relation to each other merely by the inductive condition of the particles
of matter between them, or are they in relation by some higher quality and
condition (1654.), which, acting at a distance and not by the intermediate
particles, has, like the force of gravity, no relation to them?
1664. If the latter be the case, then, when electricity is acting upon and
in matter, its direct and its transverse action are essentially different
in their nature; for the former, if I am correct, will depend upon the
contiguous particles, and the latter will not. As I have said before, this
may be so, and I incline to that view at present; but I am desirous of
suggesting considerations why it may not, that the question may be
thoroughly sifted.
1665. The transverse power has a character of polarity impressed upon it.
In the simplest forms it appears as attraction or repulsion, according as
the currents are in the same or different directions: in the current and
the magnet it takes up the condition of tangential forces; and in magnets
and their particles produces poles. Since the experiments have been made
which have persuaded me that the polar forces of electricity, as in
induction and electrolytic action (1298. 1343.), show effects at a distance
only by means of the polarized contiguous and intervening particles, I have
been led to expect that _all polar forces_ act in the same general manner;
and the other kinds of phenomena which one can bring to bear upon the
subject seem fitted to strengthen that expectation. Thus in
crystallizations the effect is transmitted from particle to particle; and
in this manner, in acetic acid or freezing water a crystal a few inches or
even a couple of feet in length will form in less than a second, but
progressively and by a transmission of power from particle to particle.
And, as far as I remember, no case of polar action, or partaking of polar
action, except the one under discussion, can be found which does not act by
contiguous particles[A]. It is apparently of the nature of polar forces
that such should be the case, for the one force either finds or developed
the contrary force near to it, and has, therefore, no occasion to seek for
it at a distance.
[A] I mean by contiguous particles those which are next to each other,
not that there is _no_ space between them. See (1616.).
1666. But leaving these hypothetical notions respecting the nature of the
lateral action out of sight, and returning to the direct effects, I think
that the phenomena examined and reasoning employed in this and the two
preceding papers tend to confirm the view first taken (1464.), namely, that
ordinary inductive action and the effects dependent upon it are due to an
action of the contiguous particles of the dielectric interposed between the
charged surfaces or parts which constitute, as it were, the terminations of
the effect. The great point of distinction and power (if it have any) in
the theory is, the making the dielectric of essential and specific
importance, instead of leaving it as it were a mere accidental circumstance
or the simple representative of space, having no more influence over the
phenomena than the space occupied by it. I have still certain other results
and views respecting the nature of the electrical forces and excitation,
which are connected with the present theory; and, unless upon further
consideration they sink in my estimation, I shall very shortly put them
into form as another series of these electrical researches.
_Royal Institution.
February 14th, 1838._