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AN
EPITOME
OF
ELECTRICITY & GALVANISM.
BY TWO GENTLEMEN OF PHILADELPHIA.
Causa latet; vis est notissima.——Ovid’s Met. B. IV. l. 287.
PHILADELPHIA:
PRINTED BY JANE AITKEN, No. 71,
NORTH THIRD STREET.
1809.
DISTRICT OF PENNSYLVANIA, TO WIT:
[Sidenote: SEAL.]
_BE IT REMEMBERED_, That on the fourteenth day of December, in the
thirty-fourth year of the Independence of the United States of America,
A. D. 1809. Jane Aitken, of the said District, hath deposited in this
Office, the Title of a Book, the Right whereof she claims as Proprietor,
in the words following, _to wit_:—
“An Epitome of Electricity and Galvanism. By two gentlemen of
Philadelphia. Causa latet; vis est notissima.—Ovid’s Met. B. IV. l.
287.”
In conformity to the Act of the Congress of the United States,
intituled, “An Act for the encouragement of Learning, by securing the
Copies of Maps, Charts, and Books, to the Authors and Proprietors of
such Copies, during the times therein mentioned.” And also to the Act,
entitled “An Act, supplementary to an Act, entitled, “An Act for the
encouragement of Learning, by securing the Copies of Maps, Charts, and
Books, to the Authors and Proprietors of such Copies, during the times
therein mentioned,” and extending the benefits thereof to the Arts of
designing, engraving, and etching historical and other prints.”
D. CALDWELL, _Clerk of the
District of Pennsylvania_.
RECOMMENDATIONS.
_Having perused this Epitome, it appears to me to comprise, in a concise
and perspicuous manner, the principal discoveries that have been made in
Electricity and Galvanism, illustrated with a variety of amusing
experiments; and I have no doubt that it will prove useful and
entertaining to those who wish for information on these subjects._
_JOHN M‘DOWELL_,
Professor of Natural Philosophy, and Provost
of the University of Pennsylvania.
Philad. Dec. 11, 1809.
* * * * *
_Having read, at the request of the authors, a work under the title of_
“An Epitome of Electricity and Galvanism,” _I am of opinion that it is
well calculated for the instruction of youth; and also that it may prove
a useful manual to gentlemen who wish to acquire, without extensive
reading, a general knowledge of the subjects discussed_.
_JOHN MACLEAN_,
Professor of Natural Philosophy and Chemistry
in the College of New-Jersey.
Nassau Hall, Oct. 20, 1809.
_The Epitome of Electricity appears to me to contain a concise, but
perspicuous and correct statement of the laws of that branch of
Philosophy, and an interesting collection of facts and experiments, by
which they are illustrated._
_JEREMIAH DAY_,
Professor of Mathematics and Natural Philosophy.
Yale College, Nov. 25, 1809.
[As the authors could not transmit to Professor DAY a copy of the
Epitome of Galvanism, without unduly delaying the publication, his
testimonial, of course, refers only to the Epitome of Electricity.]
PREFACE.
Having denominated the following work an epitome of Electricity and
Galvanism, it seems reasonable to request that the reader should keep
the nature of our plan in view. If the book do not contain, on the
subjects proposed to be treated, all that is most important, let it be
condemned. But let not detail be expected where the design requires
conciseness. There are some articles under which we were obliged, either
to omit unimportant improvements, or to occupy several pages in
describing them.
Where, however, omissions of any consequence have taken place, we have
endeavoured carefully to refer to the books which will supply them; so
that our work may not only teach the elements and substance of the
science, but direct those who wish to pursue it most extensively—We
particularly regretted that we could not describe a variety of
electrometers.
Short as our work is, we found it, notwithstanding, scarcely practicable
to avoid some repetition. In a few instances the historical and
scientific parts may be observed, in a small degree, to interfere. Where
history was useful to illustrate experiment, or experiment composed a
part of history, we did not choose to separate what perspicuity required
to be kept together. We hope, on the whole, that we do not need more
indulgence in this respect, than we shall readily find, from those who
are fond of the subjects which it was our business and our pleasure to
investigate.
In making our epitome, we have often written without a special reference
to any book; sometimes we have abridged the writings of others;
sometimes we have taken paragraphs with the alteration of a few words;
and sometimes we have introduced full quotations. In the latter case, we
have always wished to make a distinct reference to the author quoted;
and in other cases, we have generally made our acknowledgments where we
were particularly indebted. But as our work was begun without any
determination to publish it, we have probably made some selections, of
which we have ourselves forgotten the authors from whom they were taken.
Of the fairness of a work of this nature, we suppose there can be no
question. Johnson, when speaking of the system of logic published by
Watts, has made our apology—“If he owes part of it to Le Clerk, it must
be considered, that no man who undertakes merely to methodise or
illustrate a system, pretends to be its author.”
As impositions are often attempted, by soliciting patronage for
publications of little value, we felt the importance of obtaining, in
behalf of our work, the approbation of competent judges—The public will
admit that it has been obtained; and the professional gentlemen who have
favoured us with it in the most obliging and disinterested manner, will
excuse our offering them this public tender of our grateful
acknowledgments.
With these remarks we commit our little work to the candour of the
public, conscious of having assiduously laboured to furnish a book
which, though it appeared to us to be much wanted, had not yet been
written or compiled. Our views will be fully answered, if it shall be
found well adapted to assist youth in their academical and philosophical
studies, and at the same time, to afford amusement to men of learning,
and some useful information to gentlemen of leisure.
INTRODUCTION.
SECTION I.
_Electricity as known among the Ancients._
In examining the progress of almost any branch of human knowledge,
curiosity must meet with many repulses. By the time the attention of
society is attracted to the accumulation of detached truths, which
compose a science, it is often impossible to retrace its history. The
real origin of most discoveries is obscured by antiquity, their authors
have already sunk into oblivion, and important improvements are ascribed
to different inventors.
Electricity is however oppressed by few of these difficulties. With the
exception of some small discoveries mentioned by ancient authors, this
science derives its origin and all its improvements from the two last
centuries. Neither is the historian perplexed in giving every invention
to its proper author. Those who cultivated this science were commonly
men of talents and condition; they pursued it with ability and
perseverance; and either themselves published the result of their
observations, or deposited them in those literary institutions which
they found established in their country. The historian of electricity,
therefore, with no extraordinary exertion of industry or talent, may
fully collect and accurately arrange the materials of his work.
On the subject of electricity nothing earlier is on record than the
observation of Thales, that yellow amber, when rubbed, has the property
of attracting light bodies.—So struck was he with this property of
amber, that he imagined it was animated.
Thales, the contemporary of Pythagoras, was born at Miletus, a city of
Ionia, about six hundred years before Christ. Like all the Grecian
sages, he travelled into Egypt; lived in that country a number of years;
contracted friendships with the priests, then the depositories of
science; and became deeply skilled in all their mysteries and learning.
Returning to his own country, stored with the knowledge of the East, he
was ranked as the first of the seven wise men of Greece, and became the
founder of the Ionic school, as Pythagoras did of the Italic.
It may deserve remark that the same philosopher who is recorded to have
observed the first phenomenon in electricity, is also said to have
discovered the cause of thunder and lightning. We shall give to the
curious, the remarkable passage containing this account, as we find it
in Apuleius, a learned and eloquent writer of the second century, while
he is rapidly enumerating the discoveries of Thales.
_Thales Milesius ex septem illis sapientia memoratis viris facile
præcipuus: fuit enim geometricæ penes Grajos primus repertor, et naturæ
rerum certissimus explorator, et astrorum peritissimus contemplator,
maximas res parvis lineis reperit, temporum ambitus, ventorum flatus,
stellarum meatus_, tonitruum sonora miracula, _siderum obliqua
curricula, Solis annula reverticula; idem Lunæ vel nascentis incrementa,
vel senescentis dispendia, vel delinquentis obstacula_.
“Thales the Milesian was decisively the most eminent of the seven famous
sages; for he was the first inventor of geometry among the Greeks, the
most judicious inquirer into nature, and the most skilful observer of
the stars; he made great discoveries by small geometrical lines, the
regulation of times and seasons, the theory of the winds, the course of
the stars, _the wonderful causes of thunder_, the oblique motions of the
planets, the annual revolution of the sun, the reason of the increase,
decrease, and eclipse of the moon.”[1]
Though it is no where expressly affirmed that electricity was discovered
by Thales to be the cause of thunder, yet when the two facts are placed
together, they will furnish an additional argument to those writers who
contend that the ancients knew much more than we are willing to allow
them of those shining truths, which are the peculiar boast of modern
ages. Nor should this early discovery, if we could admit it to be real,
excite our surprise. Whatever hindrances might impede the progress of
the ancients in other branches of knowledge, from the abstruse nature of
the subject, or the want of necessary helps, it may rather excite our
wonder, that the effects of electricity should remain so long
unobserved. The electric fluid is no local or occasional agent; it is
coeval with the world; its presence pervades every substance; it is the
principal cause of the grandest scenes in nature, and its operations can
hardly fail to show themselves wherever bodies are concerned.
From the time of Thales, there is a chasm in the history of electricity
for three hundred years. Indeed, natural science of all kind appears to
have languished, during this period. Theophrastus, who flourished 371
years before Christ, the disciple and successor of Aristotle, and he to
whom the learned are indebted for the preservation of his master’s
works, then adds one more fact to the history of electricity.
In his treatise on stones, after speaking of the attractive power of
amber, found on the coast of Liguria, he goes on to ascribe the same
properties to the lapis lyncurius, the same substance now called
tourmaline. “It possesses (says he) an attractive power like amber: and
as they say attracts not only straws and leaves, but copper also, and
iron, if in small particles.[2]”
These two discoveries of Thales and Theophrastus are all, on the subject
of electricity, that industry has been able clearly to collect from the
barren records of antiquity. Pliny indeed has observed that “amber being
rubbed with the fingers, and having thereby become warmed, attracts to
itself straws and dried leaves, in the same manner as the magnet does
iron.” He also attributes to the Lyncurium the same properties.—Solinus
and Priscian, also, make similar statements. But as these are no more
than what Thales and Theophrastus had remarked before, they are to be
considered only as a repetition of what the preceding writers had made
known, not as any addition to the information possessed on this subject.
In like manner it might be mentioned that Aristotle, Pliny, Oppian and
Claudius, were fully acquainted with the benumbing effects produced by
the touch of the Torpedo; but as they do not appear to have suspected
that these effects were produced by electricity, they cannot be
considered as communicating or possessing any additional knowledge in
regard to this powerful agent.[3]
On subjects which regard taste, or which address themselves to the
imagination, on poetry, eloquence and the fine arts, it is to the
ancients we are to look for information and the models of perfection.
But on the various branches of knowledge which depend on observation, on
experiment, on investigation, which comprehend all the parts of
mechanical philosophy, the philosophers of antiquity afford little that
is either new or just. Hurried away by the vivacity of their genius,
which their peculiar complexion invited them to cultivate, and the
particular circumstances of the age were calculated to inflame, they
investigated facts, not that by accumulated discoveries they might lay
the foundation of solid science, but so far only as they served to
support or illustrate some favourite hypothesis.
Aristotle, to whose profound and elevated genius we are accustomed to
turn for satisfactory information on so many other subjects, affords no
remarks on electricity, and little worthy of observation on most of the
branches of natural science. One, who on this point has a right to
speak, observes.—“That though there are several very sublime questions
in his physics, which he clears up in a very masterly way, yet the main,
the gross of the work is good for nothing, infelix operis summa.[4]”
From the time of Theophrastus till the beginning of the 17th century of
the christian æra, there is no unequivocal evidence that in the science
of electricity any discovery or improvement was made, except the
solitary and unimportant fact that jet, and perhaps agate, is endued
with the same power as amber, of attracting and repelling light
bodies.—Nor is it ascertained by whom, or at what particular period,
this fact was added to the slender stock of electrical knowledge which
was then possessed. And thus it appears that for the space of about 1900
years, the part of philosophy, of which we trace the history, was nearly
stationary.
SECTION II.
_Electricity as known to the Moderns._
Having seen, in the preceding section, the very limited knowledge of
electricity possessed by the ancients, we now come to give an account of
what may properly be called its real origin, and to trace its progress
to the present day. In doing this, we shall be careful to note all the
original authors who have touched upon this subject; and to exhibit most
of their discoveries.
We believe it to be generally the case, that, in the earlier periods of
a science, the mind is curious to observe the gradual developement of
principles, and the gradual increase of facts, however unimportant these
facts may afterwards appear. But as the science progresses, as the
ground widens and observations multiply, this curiosity proportionably
abates, and we require of the historian selection rather than detail.
However minute, therefore, the history of the first stages of this
branch of philosophy must be, the after periods will exact only a
careful selection of those more prominent discoveries, which show the
advances of the science and mark its gradations.
During the sixteenth century, the phenomena of magnetism having engaged
the study of philosophers, they were naturally led to bestow some
attention on substances which appeared to possess similar properties
with the load-stone. Indeed, it was not till after 1729 that the idea
was entertained, that electricity was a distinct fluid, or any thing
else than a certain property of bodies, resembling magnetism; nor was
any other meaning affixed to the word, than a power of attracting and
repelling.
Fifteen centuries having elapsed from the time of Theophrastus, William
Gilbert, physician to king James I, in 1600 published a latin work,
entitled, _De Magnete, magnetesque corporibus_, in which, having
discussed the phenomena of magnetism, he, towards the close, relates a
great variety of electrical experiments.
The principal merit of this philosopher is, that he greatly augmented
the list of electrical substances, noted the bodies on which electrics
can act, and remarked several circumstances relating to the manner of
their action.
He enumerates, as having the power of attracting light bodies, Diamonds,
Saphirs, Carbuncles, Iris, Opals, Amethysts, Beryl, Crystal,
Bristol-stones, Sulphur, Mastick, Hard Wax, Hard Rosin, Arsenic,
Sal-gemm, Rock-Alum, common-glass, Stibium, or glass of Antimony. He
also observed that the influence of these substances extended, not only
to leaves and straws, but to all matter which was not extremely rare.
Friction, he says, is, in general, necessary to excite the virtue of
these substances; and the most effectual friction, he affirms, is that
which is light and quick. Electrical appearances, he asserts, were
strongest when the air was dry, and the wind north or east, at which
time electrics would act ten minutes after excitation.
The simple experiments of this philosopher were mostly made with long
thin pieces of metal, and other substances freely suspended on their
centers, to the extremities of which he presented the electrics he had
excited.
The phenomena of magnetism were accounted for, in the time of Gilbert,
by means of emanating effluvia, and he applies the same theory to the
explanation of electrical attraction, imagining it to be performed in
the same manner as the attraction of cohesion. Two drops of water, rush
together when they are brought into contact, and electrics, he says, are
virtually brought into contact by means of their effluvia. _Effluvia
illa tenuiora concipiunt et amplectuntur corpora, quibus uniuntur, et
electris tanquam extensis brachiis, et ad fontem propinquitate,
invalescentibus effluviis, deducuntur._ “Those subtle effluvia
continually embrace certain bodies, to which they are united, as it were
by their extended electric arms; and the effluvia prevailing, the bodies
are drawn to the contiguous source of the effluvia.”
Gilbert has been stiled the father of modern electricity; and when we
consider how little was known of the subject prior to his time, and the
merit that belongs to himself, not only from his own experiments, but
also from turning the attention of philosophers to a new branch of
natural science, we cannot but allow that he eminently deserves the
title.
Cabeus followed Gilbert, but did little else than add to the list of
electrics, wax, gum elemi, Gum guaiaci, Pix Hispanica and Gypsum.
Thirty years after the publication of Gilbert’s work, the celebrated Sir
Kenelm Digby, in his “Treatise of the nature of Bodies,” touches upon
electricity: but as the age in which he lived was still busying itself
with the hypothetical philosophy of Aristotle, so this philosopher in
what he says of electricity, appears to be rather amusing himself in
inventing theories, to explain the manner in which electric attraction
is performed, than in advancing the science by new facts and
experiments. His theory of electric attraction is, however, of some
celebrity: it was allowed by his contemporary Des Cartes, in his
principles of philosophy, and was embraced by the chief writers of his
age; though it does not differ essentially from that of Gilbert.
“Attraction (says he) is made by a tenuious emanation, or continued
effluvium, which after some distance retracteth into itself, as is
observable in drops of syrups, oil and seminal viscosities, which spun
at length, retire to their dimensions. Now these effluviums advancing
from the body of an electric, in their return do carry back the bodies
whereon they have laid hold, within the sphere or circle of their
continuities; and these they do not only attract, but with their viscous
arms, hold fast a good while after. And if any shall wonder why these
effluvium issuing forth, impel and protrude not the straw before they
can bring it back; it is because the effluvium passing out in a smaller
thread, and more enlengthened filament, stirreth not the bodies
interposed; but returning into its original, falls into a closer
substance and carrieth them back into itself.”
Sir Thomas Brown succeeded to Sir Kenelm Digby. In his “Inquiry into
Vulgar Errors,” this inquisitive philosopher has a chapter on
electricity, in which he corrects some mistakes into which his
predecessor had fallen, adds some new experiments of his own, and gives
us a summary view of the state of electrical knowledge at the time he
wrote.
“By electrical bodies, (says he) I understand not such as are
metallical, mentioned by _Pliny_, and the ancients; for their _electrum_
was a mixture made of gold, with the addition of a fifth part of silver;
a substance now as unknown as true _Aurichalcum_, or _Corinthian_ brass,
and set down among things lost by _Pancirollus_. Nor by electric bodies
do I conceive such only as take up shavings, straws, and light bodies,
in which number the ancients only placed _Jet_ and _Amber_; but such as
conveniently placed unto their objects attract all bodies palpable
whatsoever. I say conveniently placed, that is, in regard of the object,
that it be not too ponderous, or any way affixed; in regard of the
agent, that it be not foul or sullied, but wiped, rubbed, and excitated;
in regard of both, that they be conveniently distant, and no impediment
interposed. I say, all bodies palpable, thereby excluding fire, which
indeed it will not attract, nor yet draw through it; for fire consumes
its effluxions by which it should attract.”
Brown augmented the list of electrics, and found attraction not only in
simple bodies, but in such also as were compounded. He observed, that
the attractions of bodies were different. Resinous bodies, he says,
attract most vigorously, and “good hard wax so powerfully, that it will
convert the needle almost as actively as the load-stone. Gums easily
dissolved in water, draw not at all; no metal attracts, nor wood, though
never so hard and polished. “Glass, (he says,) attracts but weakly,
though clear: and some slick stones, and thick glasses but
indifferently.”
These experiments on the electricities of bodies, he performed by means
of a needle, “settled freely upon a well pointed pin, so that the
electrics might be applied to it without disadvantage;” he tried them
also in straws and paleous bodies, powders of wood and iron, in gold and
silver foliated.
How the attraction of electrics is performed, he acknowledges is not
easily determined; though, he says, “that it is performed by effluviums
is plain, and granted by most; for electrics will not commonly attract,
except they grow hot and perspirable. For if they be foul and
obnubilated, it hinders their effluxion; nor if they be covered, though
but with linen or sarsenet, or if a body be interposed, for that
intercepts the _effluvium_. If also a powerful and broad electric of wax
or _anime_ be held over fine powder, the atoms or small particles will
ascend most numerously unto it; and if the electric be held unto the
light, it may be observed that many thereof will fly, and be as it were
discharged from the electric to the distance sometime of two or three
inches. Which motion is performed by the breath of the _effluvium_
issuing with agility; for as the electric cooleth, the projection of the
atoms ceaseth.”
Sir Francis Bacon in his “Physiological Remains,” has inserted a
catalogue of bodies attractive and not attractive; but he differs in
nothing worth mentioning from his predecessors.
Mr. Boyle, who so eminently distinguished himself in the latter part of
the seventeenth century, was led by the study of chemistry, to give some
attention to electricity. He enlarged the catalogue of electrics; and
noticed some circumstances relating to electrical attraction, which had
escaped former philosophers. The electrical properties of bodies he
found were increased by wiping and warming them, before they were
rubbed. Bodies of all kinds, he observed, were indiscriminately
attracted; and this attraction he supposed took place in vacuo as well
as in the open air.
Hitherto the attraction of electrics was the single phenomenon noticed
by philosophers. Gilbert, even when remarking on the characteristic
differences between magnetism and electricity, observes, that in
magnetism there is both attraction and repulsion, but in electricity
only the latter, and not the former.[5] Boyle made an approach to the
discovery of this fact of electrical repulsion, by remarking that light
bodies, as feathers &c. would cling to his fingers and other substances,
after they had been attracted by electrics.
Otto Guericke, the celebrated inventor of the air pump, who was
contemporary with Mr. Boyle, improved the science much farther. He made
use of a sulphur globe, whirled on an axis, much in the same way with
our present glass globes. He could thus excite the electricity with
greater power, and try all the experiments of his predecessors to
greater advantage. His was the full discovery of electric repulsion. “A
body once attracted, he remarks, by an excited electric, is repelled by
it, and not attracted again till it has been touched by some other
body.” In this manner he kept a feather a long time suspended in the
air, above his sulphur globe. He also made another remarkable discovery,
which has since been very generally overlooked; namely, that a feather,
when repelled by an excited electric, always keeps the same face towards
the body which repels it, as the moon does to the earth. The electric
light was probably observed by Mr. Boyle in the diamond; but Otto
Guericke saw it more clearly in the excitation of his glass globe, and
also heard the hissing sound which attends it. As this light, however,
was exhibited to Dr. Wall, about the same time, in a much finer manner,
we shall rather give his account of it.
“I found, says he, upon swiftly drawing a well polished piece of amber
in the dark, through a piece of woollen cloth, and squeezing it pretty
hard with my hand, a prodigious number of little cracklings were heard,
and every one of them produced a flash of light; but when the amber was
drawn gently and slightly through the cloth, it produced only a light,
but no crackling; but by holding one’s finger at a little distance from
the amber, a large crackling is produced, with a great flash of light
succeeding it. And, what to me is very surprising, upon its eruption, it
strikes the finger very sensibly, wheresoever applied, with a push or
puff, like wind. This light and crackling seems, in some respects, to
represent thunder and lightning.
Sir Isaac Newton is the next in chronological order, who made any
discovery of importance. He first observed that the electrical
attraction and repulsion, penetrated through glass. It cannot but be
lamented, that this great philosopher, among the vast variety of
important subjects which he cultivated and improved, had not applied
himself to electricity, with greater assiduity.
Mr. Hawksbee, in 1709, wrote a treatise on electricity, and
distinguished himself by discoveries which far surpassed those of his
predecessors. Besides a variety of new facts in regard to attraction and
repulsion, he observed the electric light distinctly, and made some
delicate and curious experiments on its nature.
The electric light was considered by Mr. Hawksbee, as well as by all
those who first observed it, as a species of phosphorus, and all the
experiments made, were conducted under this impression.
Holding an exhausted globe within the effluvia of an excited one, he
observed a light in the former, which presently died away, if it was
kept at rest; but was revived, and continued very strong, if the
exhausted globe was kept in motion. The greatest electrical light he
produced, was when he enclosed an exhausted cylinder within one not
exhausted, and excited the outermost of them, putting them both in
motion. He observed no difference, whether the globes were turned in the
same direction, or otherwise.
He made many experiments to shew the extreme subtlety of the electric
light, and found out a method of rendering opaque bodies transparent. He
lined with sealing wax more than half the inside of a glass globe, and
having exhausted it, put it in motion. On applying his hand to excite
it, he saw the shape and figure of all the parts of his hand distinctly
and perfectly, on the concave superficies of the wax within. It was as
if there had been pure glass, and no wax interposed between the glass
and his hand. This lining was in many places the eighth of an inch
thick; and in some places where it did not adhere so closely to the
glass as in others, yet the light on these appeared just as on the rest.
He repeated these experiments with pitch instead of sealing wax, and
with equal success. It is to be regretted that these facts have not
engaged more of the attention of philosophers.
After the death of Mr. Hawksbee, twenty years elapsed before any farther
improvements were made. The great discoveries which were then making in
other branches of philosophy, by Sir Isaac Newton, so absorbed the
public attention, that electricity was entirely overlooked. Mr. Grey,
after this long interval, took up the subject, and by his discovery of
the distinction between electrics and non-electrics, formed an important
epoch in the history of electricity.
An account of this discovery of Mr. Grey, is thus abridged from the
Philosophical Transactions, by Dr. Priestley. “In the month of February
1729, Mr. Grey, after some fruitless attempts to excite an electric
power in metals, recollected a suspicion he had for some time
entertained, that as a glass tube, when excited in the dark,
communicated its light to various bodies, it might at the same time
possibly communicate to them an electricity; that is, a power of
attracting light bodies; which, as yet, was all that was understood by
the word _electricity_. For this purpose he provided himself with a
glass tube, three feet five inches long, and near one inch and
two-tenths in diameter. To each end was fitted a cork; to keep the dust
out when the tube was not in use. His first experiments were made with a
view to determine whether a tube would attract equally well with the
ends shut, as with them open. In this respect there was no difference;
but he found that the corks attracted and repelled light substances, as
well, and rather better than the tube itself. He then fixed an ivory
ball upon a stalk of fir about four inches long, and thrusting the end
of the stalk into one of the corks, he found the ball endowed with a
strong attractive and repulsive virtue. This experiment he repeated in
many different ways; fixing the ball upon long sticks, and upon pieces
of brass and iron wire, always with the same success; but he constantly
observed, that the ball at the end attracted more vigorously, than that
part of the wire nearest the tube.
“The inconvenience of using long wires in this manner, put Mr. Grey upon
trying whether the ball might be suspended by a pack-thread, with a loop
on the tube, with equal success; and the event fully answered his
expectation. Having thus suspended bodies of the greatest length he
conveniently could, to his tube, he ascended a balcony 26 feet high, and
fastening a string to his tube, found that the ball would attract light
bodies on the ground below. This experiment succeeded in the greatest
heights to which he could ascend; after which, he attempted to carry the
electricity horizontally. His first attempt miscarried, because he
suspended his line, which was intended to carry the electricity
horizontally, by a pack-thread; and thus the fluid got off from it; but
though Mr. Grey knew this was the case, he could not at any time think
of any method to prevent it.
“On the 30th June 1729, Mr. Grey paid a visit to Mr. Wheeler, in order
to give him a specimen of his experiments; but told him of the
unsuccessful attempt he had made to carry the electric fluid
horizontally; Mr. Wheeler proposed to suspend the conducting line by
_silk_ instead of _pack-thread_. For this advice he could give no
reason, but that the silk thread was _smaller_ than the other; however,
with it they succeeded perfectly well. Their first experiment was in a
matted gallery at Mr. Wheeler’s house, on the 2d of July 1729. About
four feet from the end of the gallery they fastened a line across the
place. The middle of this line was silk, the rest pack-thread. Over the
silken part they laid one end of the conducting line, to which was
fastened the ivory ball, and which hung down about nine feet below the
line stretched across the gallery. The conducting line was about 80 1–2
feet in length, and the other end of it was fastened by a loop to the
electric tube. Upon rubbing the tube, the ivory ball attracted and
repelled light substances, as the tube itself would have done. They next
contrived to return the line, so that the whole length of it amounted to
147 feet; which also answered pretty well. But suspecting that the
attraction would be stronger, without doubling or returning the line,
they made use of one carried straight forward, for 124 feet; and as they
expected, found the attraction in this manner, stronger than when the
lines had been doubled. Thus they proceeded with their experiments;
still adding more conducting line, till at last their silk string broke
with the weight. This they endeavoured to supply, first with a small
iron wire, and then with a brass one. The result of these experiments,
however, soon convinced them, that the silk refused to conduct the
electric fluid, not on account of its _smallness_, as they had supposed,
but on account of some difference in the matter. The wires were smaller
than the silk threads, yet the electricity was effectually carried off
by them. They had recourse, therefore, to thicker lines of silk; and
thus conveyed the electric matter to the distance of 765 feet: nor did
they perceive the virtue to be at all diminished by the distance to
which it was carried.” In the manner in which silk was found to be a
non-conductor, the same quality was also discovered in many other
substances, such as hair, rosin, &c.
Mr. Grey also made many electrical experiments on fluids and animal
bodies. As he knew no other method of trying whether bodies were
electrified or not, but by making them raise light bodies placed under
them, to put a fluid in this situation, he dissolved soap in Thames
water, and suspending a tobacco pipe, he blew a bubble at the head of
it; and bringing the excited tube near the small end, he found the
bubble to attract leaf brass to the height of two and of four inches.[6]
He contrived afterwards, by a curious experiment to shew the effects of
electricity upon water, in a more satisfactory manner. He filled a small
cup with water higher than the brim, and when he had held an excited
tube over it, at the distance of about an inch or two, he says, that if
it were a large tube there would first arise a little mountain of water
from the top of it, of a conical form; from the vertex of which there
proceeded a light, very visible when the experiment was performed in a
dark room, and a snapping noise almost like that which was made when the
finger was held near the tube, but not quite so loud, and of a more flat
sound. Upon this, says he, immediately the mountain, if I may so call
it, falls into the rest of the water, and puts it into a tremulous and
waving motion. This experiment he repeated in the sun-shine, when he
perceived small particles of water thrown from the top of the mountain;
and sometimes a fine stream of water would arise from the vertex of the
cone, in the manner of a fountain, from which issued a fine stream or
vapour, whose particles were so small as not to be seen. This last
circumstance he inferred, from the under side of the tube being wet. And
by after experiments, he found that though the cylinder of water does
not always rise, yet that there is always a stream of particles thrown
on the tube, and sometimes to such a degree as to become visible.
In April 1730, Mr. Grey suspended a boy on hair lines, in a horizontal
position, just as all electricians had before been used to suspend their
hempen lines of communication, and their wooden rods; then bringing the
excited tube near his feet, he found that leaf brass was attracted by
his head, with a vigour sufficient to raise it to the height of eight,
and sometimes of ten inches. When the leaf brass was put under his feet,
and the tube brought near his head, the attraction was small; and when
the leaf brass was brought under his head, there was no attraction at
all. While the boy was thus suspended, Mr. Grey amused himself with
making the electricity operate on several parts of his body at the same
time, and at the ends of long rods, which he made him hold in his hands,
and in diversifying the experiments several other ways.
Mr. Grey continued to study electricity as long as he lived; and besides
giving a set of fanciful experiments, by which he supposed he had
discovered a perpetual attractive power in electrics, he, a little while
before his death, entered on another course by which he hoped he should
be able to astonish the world with a new sort of planetarium. “I have
lately made (says he) several new experiments upon the projectile and
pendulous motions of small bodies by electricity; by which small bodies
may be made to move about large ones, either in circles or ellipses, and
those either concentric or excentric to the centre of the large body
about which they move, so as to make many revolutions about them. And
this motion will constantly be the same way that the planets move round
the sun, viz. from the right hand to the left, or from west to east. But
these little planets, if I may so call them, move much faster in their
apogean, than in the perigean part of their orbits; which is directly
contrary to the motion of the planets round the sun.” The manner in
which these experiments were made, as delivered by him on his death-bed
to Dr. Mortimer, was as follows: “Place a small iron globe (said he) of
an inch or an inch and a half in diameter, on the middle of a circular
cake of rosin, seven or eight inches in diameter, greatly excited; and
then a light body, suspended by a very fine thread, five or six inches
long, held in the hand over the centre of the cake, will, of itself,
begin to move in a circle round the iron globe, and constantly from west
to east. If the globe is placed at any distance from the centre of the
circular cake, it will describe an ellipse, which will have the same
excentricity as the distance of the globe from the centre of the cake.
If the cake of rosin be of an elliptical form, and the iron globe be
placed in the centre of it, the light body will describe an elliptical
orbit, of the same excentricity with the form of the cake. If the globe
be placed in or near one of the foci of the elliptical cake, the light
body will move much swifter in the apogee, than in the perigee of its
orbit. If the iron globe is fixed on a pedestal an inch from the table,
and a glass hoop, or a portion of a hollow glass cylinder excited, be
placed round it, the light body will move as in the circumstance
mentioned above, and with the same varieties.” He said, moreover, that
the light body would make the same revolutions, only smaller, round the
iron globe placed on the bare table, without any electrical substance to
support it: but he acknowledged that he had not found the experiment
succeed if the thread was supported by any thing but the human hand;
though he imagined any other animal substance would have answered the
purpose.
These experiments occasioned a great deal of speculation. Dr. Mortimer
was the only person who was able to repeat them with success, and he
only when nobody but himself was the witness. It was therefore generally
supposed that both he and Mr. Grey had been deceived: but from some
experiments to be related hereafter, it seems probable that the success
of Mr. Grey and Dr. Mortimer was owing to their having performed their
experiments with candle-light; and the failure of the others to their
having attempted them by day light. Notwithstanding which, it is more
than probable that Mr. Grey has been deceived in a number of
particulars; for no motion can be performed by an artificial excitation
of the electric fluid, but what is attended with much irregularity.
Not long after the discovery of Mr. Grey of the difference between
conductors and non-conductors, Mr. Du Fay, a French philosopher, (for
the “spirit of electricity” had passed from England to France,)
discovered, what was afterwards called positive and negative
electricity; or as he denominated them the vitreous and resinous
electricities. “Chance (says he) has thrown in my way a principle, which
casts a new light on the subject of electricity. The principle is, that
there are two distinct kinds of electricity, very different from one
another, one of which I call vitreous, and the other resinous
electricity. The first is that of glass, rock crystal, precious stones,
hair of animals, wool and many other bodies. The second is that of
amber, copal, gum lac, silk thread, paper, and a vast number of other
substances. The characteristics of these two electricities is, that they
repel themselves and attract each other. Thus a body of the vitreous
electricity repels the vitreous, and on the contrary attracts all those
of the resinous. The resinous also repels the resinous and attracts the
vitreous. This discovery of Mr. Du Fay was made in consequence of his
casually observing, that a piece of leaf gold, repelled by an excited
glass tube, and which he meant to chace about the room with a piece of
excited gum copal, instead of being repelled by it, as it was by the
glass tube, was eagerly attracted.
This doctrine of two different electricities, produced by exciting
different substances, was dropped after Mr. Du Fay; and even this
philosopher himself adopted at last the opinion of Dr. Franklin that the
two electricities differ only in degree, and that the stronger attracts
the weaker. Although many of the experiments of Mr. Grey led directly to
it, yet to the French philosopher just mentioned, belongs the merit of
first drawing the electrical spark from the human body.—And we cannot
forbear remarking, in this place on the regular and progressive advances
which the human mind makes in the investigation of science. Electrical
attraction was, for a long period, the single phenomenon known to
philosophers.—Repulsion was then observed to be also a property of
electrics.—In the investigation of these we read of the accidental
discovery of the electric light.—To this naturally succeeded, Mr. Grey’s
distinction between conductors and non-conductors; and then the
difference between vitreous and resinous electricities by Mr. Du Fay. We
shall have to remark in the sequel of this history, how each succeeding
fact and invention grew out of that which immediately preceded it.
The knowledge of electricity did not stop in France. The Germans began
to labour in the same field; and with laudable success. Their success
arose chiefly from the improvements they made in the electrical
apparatus. The simple experiments of Gilbert, and the early
electricians, were made by exciting a piece of amber or sulphur. Mr.
Boyle found the electric power increased by smoothing the surface of
bodies. Otto Guericke made his experiment with a _globe of sulphur_,
formed by melting that substance in a hollow globe of glass, and
afterwards breaking the glass from off it, little supposing that the
glass itself would better have answered his intention. In 1709 Mr.
Hawksbee first observed the great electric power of glass. He used a
_glass globe_, which he mounted upon an axis, whirling it round, and at
the same time applying his hand to it. He also, to increase the power,
inclosed an exhausted cylinder within another, exciting the outermost.
After Mr. Hawksbee’s death, the glass globe was laid aside, and his
successors confined themselves to the use of _tubes_. Mr. Boze,
professor of philosophy at Wittemburgh, in 1742 returned to the use of
the _globe_. He also added a _prime-conductor_ of tin or iron,
supported, at first, by a man standing on cakes of rosin, but afterwards
by silken lines extended horizontally, under the conductor. Mr.
Winckler, of Leipsic, to excite the globe, substituted a _cushion_,
instead of the hand. The electrical _star_ and the electrical _bells_
were also the invention of the German philosophers. Dr. Desagulier,
likewise, assisted electricians by some electrical terms. He first gave
to bodies conveying electricity the name of _conductors_; and those in
which electricity may be excited by heating and rubbing he calls
_electrics per se_.
In 1745, the attention of Dr. Watson being attracted by the account of
the Germans having fired spirits of wine, he applied himself to
electricity with much assiduity, and made many valuable and curious
discoveries. But though his improvements were considerable, and such as
at another time would have excited interest, they were now lost amid the
surprise occasioned by the most remarkable discovery that had yet been
made in the whole science. This was the accumulation of the electric
matter in glass bottles, and the method of giving the electric shock.
The merit of this discovery belongs to Mr. Cuneus, a native of Leyden,
from whence it derives its name of the Leyden phial.[7] “M.
Muschenbroeck, professor in the university in that city, observing with
his friends, that electrified bodies, exposed to the common atmosphere,
which is always replete with conducting particles of various kinds, soon
lost their electricity, and were capable of retaining but a small
quantity of it, imagined, that were the electrified bodies terminated on
all sides by original electrics, they might be capable of receiving a
stronger power, and retaining it a longer time. Glass being the most
convenient electric for this purpose, and water the most convenient
non-electric, they first made their experiments with water in glass
bottles; but no considerable discovery was made, till the professor, or
Mr. Cuneus, happening to hold his glass vessel in one hand, containing
water, which had a communication with the prime-conductor by means of a
wire, and with the other hand disengaging it from the conductor (when he
imagined the water had received as much electricity as the machine could
give) was surprised by a sudden shock in his arms and breast, which he
had not in the least expected from the experiment.”
Wonder is the effect of ignorance, and ignorance begets credulity; but
when wonder and credulity are coupled with terror and surprise, we must
look for a strange and mishapen progeny. The exaggerated accounts of
those who first experienced the electric shock cannot but raise a smile;
especially as we may ascertain their real sensations by like experiments
upon ourselves.