In his famous letter of March 20, 1800, written in French from Como,
Italy, to the president of the Royal Society in London, Volta made the
first public announcement of both his "pile" (the first English
translator used the word "column"), and his "crown of cups" (the same
translator used "chain of cups" for Volta's "couronne de tasses"). The
former consisted of a vertical pile of circular disks, in which the
sequence copper-zinc-pasteboard, was repeated 10 or 20 or even as many
as 60 times, the pasteboard being moistened with salt water. The "crown
of cups" could be most conveniently made with drinking glasses, said
Volta, with separated inch-square plates of copper and zinc in salt
water in each glass, the copper sheet in one glass being joined by some
intermediate conductor and soldered joints to the zinc in the next
glass.
Volta considered the "crown of cups" and the "pile" to be essentially
identical, and as evidences of the electrical nature of the latter,
said:
... if it contains about 20 of these stories or couples of metal, it
will be capable not only of emitting signs of electricity by
Cavallo's electrometer, assisted by a condenser, beyond 10° or 15°,
and of charging this condenser by mere contact so as to make it emit
a spark, etc., but of giving to the fingers with which its
extremities (the bottom and top of the column) have been touched
several small shocks, more or less frequent, according as the
touching has been repeated. Each of these shocks has a perfect
resemblance to that slight shock experienced from a Leyden flask
weakly charged, or a battery still more weakly charged, or a torpedo
in an exceedingly languishing state, which imitates still better the
effects of my apparatus by the series of repeated shocks which it
can continually communicate.[4]
The "effects" provided by Volta's pile and crown-of-cups are therefore
electroscope deflection, sparks, and shocks. Later in the letter, he
describes the stimulation of sight, taste, and hearing as noted earlier,
but nowhere does he mention chemical phenomena of any kind, or the
heating of a wire joining the terminals of either device. Hence, except
for the additional physiological responses, he adds nothing to the
catalog of observations on which instruments might be based. His
familiarity with the moods of the torpedo (electric eel) seems to be
intimate.
The reading of Volta's letter to the Royal Society on June 26, 1800, its
publication in the Society's _Philosophical Transactions_ (in French)
immediately thereafter, and its publication in English in the
_Philosophical Magazine_ for September 1800,[5] gave scientists
throughout Europe an easily constructed and continuously operating
electric generator with which innumerable new physical, chemical, and
physiological experiments could be made. Editor-engineer William
Nicholson read Volta's letter before its publication and, by the end of
April, he and surgeon Anthony Carlisle had built a voltaic pile.
Applying a drop of water to improve the "connection" of a wire lying on
a metal plate, they happened to notice gas bubbles forming on the wire,
and pursued the observation to the point of identifying the electrical
decomposition of water into hydrogen and oxygen.
Within two or three years innumerable electrochemical reactions had been
described, some of which, one might think, could have served as
operating principles for electrical instruments. Although the phenomena
of gas formation and metal deposition were in fact widely used as crude
indicators of the polarity and relative strength of voltaic piles and
chemical cells during the period 1800-1820 (and the gas bubbles were
made the basis of a telegraph receiver by S. T. Soemmering), the
quantitative laws of electrolysis were not worked out by Faraday until
after 1830, and not until 1834 was he satisfied that the electrolytic
decomposition of water was sufficiently well understood to be made the
basis for a useful measuring instrument. Describing his
water-electrolysis device in that year, he wrote:
The instrument offers the only _actual measurer_ [italics his] of
voltaic electricity which we at present possess. For without being
at all affected by variations in time or intensity, or alterations
in the current itself, of any kind, or from any cause, or even of
intermissions of actions, it takes note with accuracy of the
quantity of electricity which has passed through it, and reveals
that quantity by inspection; I have therefore named it a
VOLTAELECTROMETER.[6]
In passing, Faraday commented that the efforts by Gay-Lussac and Thenard
to use chemical decomposition as a "measure of the electricity of the
voltaic pile" in 1811 had been premature because the "principles and
precautions" involved were not then known. He also noted that the
details of _metal deposition_ in electrolysis were still not
sufficiently understood to permit its use in an instrument.[7]
The heating of the wires in electric circuits must have been observed so
early and so often with both electrostatic and voltaic apparatus, that
no one has bothered to claim or trace priorities for this "effect." The
production of incandescence, however, and the even more dramatic
combustion or "explosion" of metal-foil strips and fine wires has a good
deal of recorded history. Among the first to burn leaf metal with a
voltaic pile was J. B. Tromsdorff of Erfurt who noted in 1801 the
distinctly different colors of the flames produced by the various common
metals. In the succeeding few years, Humphry Davy at the Royal
Institution frequently, in his public lectures, showed wires glowing
from electric current.
Early electrical instrumentation based on the heating effect took an
unusual form. Shortly after 1800, W. H. Wollaston, an English M.D.,
learned a method for producing malleable platinum. He kept the process
secret, and for several years enjoyed an extremely profitable monopoly
in the sale of platinum crucibles, wire, and other objects. About 1810,
he invented a technique for producing platinum wire as fine as a few
millionths of an inch in diameter, that has since been known as
"Wollaston wire." For several years preceding 1820, no other instrument
could compare the "strengths" of two voltaic cells better than the test
of the respective maximum lengths of this wire that they could heat to
fusion. One can sympathize with Cumming's comment in 1821 about "the
difficulty in soldering wires that are barely visible."[8]