A: Physiological Effects
B: Magnetic Deflection.
C: Magnets made.
D: Spark.
E: Heating Power.
F: True chemical Action.
G: Attraction and Repulsion.
H: Discharge by Hot Air.
_________________________________________________________
| | | | | | | | | |
| | A | B | C | D | E | F | G | H |
|_________________________|___|___|___|___|___|___|___|___|
| | | | | | | | | |
| 1. Voltaic electricity | X | X | X | X | X | X | X | X |
|_________________________|___|___|___|___|___|___|___|___|
| | | | | | | | | |
| 2. Common electricity | X | X | X | X | X | X | X | X |
|_________________________|___|___|___|___|___|___|___|___|
| | | | | | | | | |
| 3. Magneto-Electricity | X | X | X | X | X | X | X | |
|_________________________|___|___|___|___|___|___|___|___|
| | | | | | | | | |
| 4. Thermo-Electricity | X | X | + | + | + | + | | |
|_________________________|___|___|___|___|___|___|___|___|
| | | | | | | | | |
| 5. Animal Electricity | X | X | X | + | + | X | | |
|_________________________|___|___|___|___|___|___|___|___|
[A] Many of the spaces in this table originally left blank may now be
filled. Thus with _thermo-electricity_, Botto made magnets and
obtained polar chemical decomposition: Antinori produced the spark;
and if it has not been done before, Mr. Watkins has recently heated a
wire in Harris's thermo-electrometer. In respect to _animal
electricity_, Matteucci and Linari have obtained the spark from the
torpedo, and I have recently procured it from the gymnotus: Dr. Davy
has observed the heating power of the current from the torpedo. I have
therefore filled up these spaces with crosses, in a different position
to the others originally in the table. There remain but five spaces
unmarked, two under _attraction_ and _repulsion_, and three under
_discharge by hot air_; and though these effects have not yet been
obtained, it is a necessary conclusion that they must be possible,
since the _spark_ corresponding to them has been procured. For when a
discharge across cold air can occur, that intensity which is the only
essential additional requisite for the other effects must be
present.--_Dec. 13 1838._
§ 8. _Relation by Measure of common and voltaic Electricity._[A]
[A] In further illustration of this subject see 855-873 in Series
VII.--_Dec. 1838._
361. Believing the point of identity to be satisfactorily established, I
next endeavoured to obtain a common measure, or a known relation as to
quantity, of the electricity excited by a machine, and that from a voltaic
pile; for the purpose not only of confirming their identity (378.), but
also of demonstrating certain general principles (366, 377, &c.), and
creating an extension of the means of investigating and applying the
chemical powers of this wonderful and subtile agent.
362. The first point to be determined was, whether the same absolute
quantity of ordinary electricity, sent through a galvanometer, under
different circumstances, would cause the same deflection of the needle. An
arbitrary scale was therefore attached to the galvanometer, each division
of which was equal to about 4°, and the instrument arranged as in former
experiments (296.). The machine (290.), battery (291.), and other parts of
the apparatus were brought into good order, and retained for the time as
nearly as possible in the same condition. The experiments were alternated
so as to indicate any change in the condition of the apparatus and supply
the necessary corrections.
363. Seven of the battery jars were removed, and eight retained for present
use. It was found that about forty turns would fully charge the eight jars.
They were then charged by thirty turns of the machine, and discharged
through the galvanometer, a thick wet string, about ten inches long, being
included in the circuit. The needle was immediately deflected five
divisions and a half, on the one side of the zero, and in vibrating passed
as nearly as possible through five divisions and a half on the other side.
364. The other seven jars were then added to the eight, and the whole
fifteen charged by thirty turns of the machine. The Henley's electrometer
stood not quite half as high as before; but when the discharge was made
through the galvanometer, previously at rest, the needle immediately
vibrated, passing _exactly_ to the same division as in the former instance.
These experiments with eight and with fifteen jars were repeated several
times alternately with the same results.
365. Other experiments were then made, in which all the battery was used,
and its charge (being fifty turns of the machine,) sent through the
galvanometer: but it was modified by being passed sometimes through a mere
wet thread, sometimes through thirty-eight inches of thin string wetted by
distilled water, and sometimes through a string of twelve times the
thickness, only twelve inches in length, and soaked in dilute acid (298.).
With the thick string the charge passed at once; with the thin string it
occupied a sensible time, and with the thread it required two or three
seconds before the electrometer fell entirely down. The current therefore
must have varied extremely in intensity in these different cases, and yet
the deflection of the needle was sensibly the same in all of them. If any
difference occurred, it was that the thin string and thread caused greatest
deflection; and if there is any lateral transmission, as M. Colladon says,
through the silk in the galvanometer coil, it ought to have been so,
because then the intensity is lower and the lateral transmission less.
366. Hence it would appear that _if the same absolute quantity of
electricity pass through the galvanometer, whatever may be its intensity,
the dejecting force upon the magnetic needle is the same._
367. The battery of fifteen jars was then charged by sixty revolutions of
the machine, and discharged, as before, through the galvanometer. The
deflection of the needle was now as nearly as possible to the eleventh
division, but the graduation was not accurate enough for me to assert that
the arc was exactly double the former arc; to the eye it appeared to be so.
The probability is, that _the deflecting force of an electric current is
directly proportional to the absolute quantity of electricity passed_, at
whatever intensity that electricity may be[A].
[A] The great and general value of the galvanometer, as an actual
measure of the electricity passing through it, either continuously or
interruptedly, must be evident from a consideration of these two
conclusions. As constructed by Professor Ritchie with glass threads
(see Philosophical Transactions, 1830, p. 218, and Quarterly Journal
of Science, New Series, vol. i. p.29.), it apparently seems to leave
nothing unsupplied in its own department.
368. Dr. Ritchie has shown that in a case where the intensity of the
electricity remained the same, the deflection of the magnetic needle was
directly as the quantity of electricity passed through the galvanometer[A].
Mr. Harris has shown that the _heating_ power of common electricity on
metallic wires is the same for the same quantity of electricity whatever
its intensity might have previously been[B].
[A] Quarterly Journal of Science, New Series, vol. i. p. 33.
[B] Plymouth Transactions, page 22.
369. The next point was to obtain a _voltaic_ arrangement producing an
effect equal to that just described (367.). A platina and a zinc wire were
passed through the same hole of a draw-plate, being then one eighteenth of
an inch in diameter; these were fastened to a support, so that their lower
ends projected, were parallel, and five sixteenths of an inch apart. The
upper ends were well-connected with the galvanometer wires. Some acid was
diluted, and, after various preliminary experiments, that adopted as a
standard which consisted of one drop strong sulphuric acid in four ounces
distilled water. Finally, the time was noted which the needle required in
swinging either from right to left or left to right: it was equal to
seventeen beats of my watch, the latter giving one hundred and fifty in a
minute. The object of these preparations was to arrange a voltaic
apparatus, which, by immersion in a given acid for a given time, much less
than that required by the needle to swing in one direction, should give
equal deflection to the instrument with the discharge of ordinary
electricity from the battery (363. 364.); and a new part of the zinc wire
having been brought into position with the platina, the comparative
experiments were made.
370. On plunging the zinc and platina wires five eighths of an inch deep
into the acid, and retaining them there for eight beats of the watch,
(after which they were quickly withdrawn,) the needle was deflected, and
continued to advance in the same direction some time after the voltaic
apparatus had been removed from the acid. It attained the five-and-a-half
division, and then returned swinging an equal distance on the other side.
This experiment was repeated many times, and always with the same result.
371. Hence, as an approximation, and judging from _magnetic force_ only at
present (376.), it would appear that two wires, one of platina and one of
zinc, each one eighteenth of an inch in diameter, placed five sixteenths of
an inch apart and immersed to the depth of five eighths of an inch in acid,
consisting of one drop oil of vitriol and four ounces distilled water, at a
temperature about 60°, and connected at the other extremities by a copper
wire eighteen feet long and one eighteenth of an inch thick (being the wire
of the galvanometer coils), yield as much electricity in eight beats of my
watch, or in 8/150ths of a minute, as the electrical battery charged by
thirty turns of the large machine, in excellent order (363. 364.).
Notwithstanding this apparently enormous disproportion, the results are
perfectly in harmony with those effects which are known to be produced by
variations in the intensity and quantity of the electric fluid.
372. In order to procure a reference to _chemical action_, the wires were
now retained immersed in the acid to the depth of five eighths of an inch,
and the needle, when stationary, observed; it stood, as nearly as the
unassisted eye could decide, at 5-1/3 division. Hence a permanent
deflection to that extent might be considered as indicating a constant
voltaic current, which in eight beats of my watch (369.) could supply as
much electricity as the electrical battery charged by thirty turns of the
machine.
373. The following arrangements and results are selected from many that
were made and obtained relative to chemical action. A platina wire one
twelfth of an inch in diameter, weighing two hundred and sixty grains, had
the extremity rendered plain, so as to offer a definite surface equal to a
circle of the same diameter as the wire; it was then connected in turn with
the conductor of the machine, or with the voltaic apparatus (369.), so as
always to form the positive pole, and at the same time retain a
perpendicular position, that it might rest, with its whole weight, upon the
test paper to be employed. The test paper itself was supported upon a
platina spatula, connected either with the discharging train (292.), or
with the negative wire of the voltaic apparatus, and it consisted of four
thicknesses, moistened at all times to an equal degree in a standard
solution of hydriodate of potassa (316.).
374. When the platina wire was connected with the prime conductor of the
machine, and the spatula with the discharging train, ten turns of the
machine had such decomposing power as to produce a pale round spot of
iodine of the diameter of the wire; twenty turns made a much darker mark,
and thirty turns made a dark brown spot penetrating to the second thickness
of the paper. The difference in effect produced by two or three turns, more
or less, could be distinguished with facility.
375. The wire and spatula were then connected with the voltaic apparatus
(369.), the galvanometer being also included in the arrangement; and, a
stronger acid having been prepared, consisting of nitric acid and water,
the voltaic apparatus was immersed so far as to give a permanent deflection
of the needle to the 5-1/3 division (372.), the fourfold moistened paper
intervening as before[A]. Then by shifting the end of the wire from place
to place upon the test paper, the effect of the current for five, six,
seven, or any number of the beats of the watch (369.) was observed, and
compared with that of the machine. After alternating and repeating the
experiments of comparison many times, it was constantly found that this
standard current of voltaic electricity, continued for eight beats of the
watch, was equal, in chemical effect, to thirty turns of the machine;
twenty-eight revolutions of the machine were sensibly too few.
[A] Of course the heightened power of the voltaic battery was
necessary to compensate for the bad conductor now interposed.
376. Hence it results that both in _magnetic deflection_ (371.) and in
_chemical force_, the current of electricity of the standard voltaic
battery for eight beats of the watch was equal to that of the machine
evolved by thirty revolutions.
377. It also follows that for this case of electro-chemical decomposition,
and it is probable for all cases, that the _chemical power, like the
magnetic force_ (36.), _is in direct proportion to the absolute quantity
of electricity_ which passes.
378. Hence arises still further confirmation, if any were required, of the
identity of common and voltaic electricity, and that the differences of
intensity and quantity are quite sufficient to account for what were
supposed to be their distinctive qualities.
379. The extension which the present investigations have enabled me to make
of the facts and views constituting the theory of electro-chemical
decomposition, will, with some other points of electrical doctrine, be
almost immediately submitted to the Royal Society in another series of
these Researches.
_Royal Institution,
15th Dec. 1832._
Note.--I am anxious, and am permitted, to add to this paper a correction of
an error which I have attributed to M. Ampère the first series of these
Experimental Researches. In referring to his experiment on the induction of
electrical currents (78.), I have called that a disc which I should have
called a circle or a ring. M. Ampère used a ring, or a very short cylinder
made of a narrow plate of copper bent into a circle, and he tells me that
by such an arrangement the motion is very readily obtained. I have not
doubted that M. Ampère obtained the motion he described; but merely mistook
the kind of mobile conductor used, and so far I described his _experiment_
erroneously.
In the same paragraph I have stated that M. Ampère says the disc turned "to
take a position of equilibrium exactly as the spiral itself would have
turned had it been free to move"; and further on I have said that my
results tended to invert the sense of the proposition "stated by M. Ampère,
_that a current of electricity tends to put the electricity of conductors
near which it passes in motion in the same direction._" M. Ampère tells me
in a letter which I have just received from him, that he carefully avoided,
when describing the experiment, any reference to the direction of the
induced current; and on looking at the passages he quotes to me, I find
that to be the case. I have therefore done him injustice in the above
statements, and am anxious to correct my error.
But that it may not be supposed I lightly wrote those passages, I will
briefly refer to my reasons for understanding them in the sense I did. At
first the experiment failed. When re-made successfully about a year
afterwards, it was at Geneva in company with M.A. De la Rive: the latter
philosopher described the results[A], and says that the plate of copper
bent into a circle which was used as the mobile conductor "sometimes
advanced between the two branches of the (horse-shoe) magnet, and sometimes
was repelled, _according_ to the direction of the current in the
surrounding conductors."
[A] Bibliothèque Universelle, xxi. p. 48.
I have been in the habit of referring to Demonferrand's _Manuel
d'Electricité Dynamique_, as a book of authority in France; containing the
general results and laws of this branch of science, up to the time of its
publication, in a well arranged form. At p. 173, the author, when
describing this experiment, says, "The mobile circle turns to take a
position of equilibrium as a conductor would do in which the current moved
in the _same direction_ as in the spiral;" and in the same paragraph he
adds, "It is therefore proved _that a current of electricity tends to put
the electricity of conductors, near which it passes, in motion in the same
direction._" These are the words I quoted in my paper (78.).
Le Lycée of 1st of January, 1832, No. 36, in an article written after the
receipt of my first unfortunate letter to M. Hachette, and before my papers
were printed, reasons upon the direction of the induced currents, and says,
that there ought to be "an elementary current produced in the same
direction as the corresponding portion of the producing current." A little
further on it says, "therefore we ought to obtain currents, moving in the
_same direction_, produced upon a metallic wire, either by a magnet or a
current. M. Ampère _was so thouroughly persuaded that such ought to be the
direction of the currents by influence_, that he neglected to assure
himself of it in his experiment at Geneva."
It was the precise statements in Demonferrand's Manuel, agreeing as they
did with the expression in M. De la Rive's paper, (which, however, I now
understand as only meaning that when the inducing current was changed, the
motion of the mobile circle changed also,) and not in discordance with
anything expressed by M. Ampère himself where he speaks of the experiment,
which made me conclude, when I wrote the paper, that what I wrote was
really his avowed opinion; and when the Number of the Lycée referred to
appeared, which was before my paper was printed, it could excite no
suspicion that I was in error.
Hence the mistake into which I unwittingly fell. I am proud to correct it
and do full justice to the acuteness and accuracy which, as far as I can
understand the subjects, M. Ampère carries into all the branches of
philosophy which he investigates.
Finally, my note to (79.) says that the Lycée, No. 36. "mistakes the
erroneous results of MM. Fresnel and Ampère for true ones," &c. &c. In
calling M. Ampère's results erroneous, I spoke of the results described in,
and referred to by the Lycée itself; but _now_ that the expression of the
direction of the induced current is to be separated, the term _erroneous_
ought no longer to be attached to them.
April 29, 1833.
M.F.]