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LITTLE MASTERPIECES OF SCIENCE
[Illustration: George Stephenson.]
Little Masterpieces
of Science
Edited by George Iles
INVENTION AND DISCOVERY
_By_
Benjamin Franklin Alexander Graham Bell
Michael Faraday Count Rumford
Joseph Henry George Stephenson
[Illustration]
NEW YORK
DOUBLEDAY, PAGE & COMPANY
1902
Copyright, 1902, by Doubleday, Page & Co.
Copyright, 1877, by George B. Prescott
Copyright, 1896, by S. S. McClure Co.
Copyright, 1900, by Doubleday, McClure & Co.
PREFACE
To a good many of us the inventor is the true hero for he multiplies the
working value of life. He performs an old task with new economy, as when
he devises a mowing-machine to oust the scythe; or he creates a service
wholly new, as when he bids a landscape depict itself on a photographic
plate. He, and his twin brother, the discoverer, have eyes to read a
lesson that Nature has held for ages under the undiscerning gaze of
other men. Where an ordinary observer sees, or thinks he sees,
diversity, a Franklin detects identity, as in the famous experiment here
recounted which proves lightning to be one and the same with a charge of
the Leyden jar. Of a later day than Franklin, advantaged therefor by new
knowledge and better opportunities for experiment, stood Faraday, the
founder of modern electric art. His work gave the world the dynamo and
motor, the transmission of giant powers, almost without toll, for two
hundred miles at a bound. It is, however, in the carriage of but
trifling quantities of motion, just enough for signals, that electricity
thus far has done its most telling work. Among the men who have created
the electric telegraph Joseph Henry has a commanding place. A short
account of what he did, told in his own words, is here presented. Then
follows a narrative of the difficult task of laying the first Atlantic
cables, a task long scouted as impossible: it is a story which proves
how much science may be indebted to unfaltering courage, to faith in
ultimate triumph.
To give speech the wings of electricity, to enable friends in Denver and
New York to converse with one another, is a marvel which only
familiarity places beyond the pale of miracle. Shortly after he
perfected the telephone Professor Bell described the steps which led to
its construction. That recital is here reprinted.
A recent wonder of electric art is its penetration by a photographic ray
of substances until now called opaque. Professor Roentgen's account of
how he wrought this feat forms one of the most stirring chapters in the
history of science. Next follows an account of the telegraph as it
dispenses with metallic conductors altogether, and trusts itself to that
weightless ether which brings to the eye the luminous wave. To this
succeeds a chapter which considers what electricity stands for as one of
the supreme resources of human wit, a resource transcending even flame
itself, bringing articulate speech and writing to new planes of facility
and usefulness. It is shown that the rapidity with which during a single
century electricity has been subdued for human service, illustrates that
progress has leaps as well as deliberate steps, so that at last a gulf,
all but infinite, divides man from his next of kin.
At this point we pause to recall our debt to the physical philosophy
which underlies the calculations of the modern engineer. In such an
experiment as that of Count Rumford we observe how the corner-stone was
laid of the knowledge that heat is motion, and that motion under
whatever guise, as light, electricity, or what not, is equally beyond
creation or annihilation, however elusively it may glide from phase to
phase and vanish from view. In the mastery of Flame for the superseding
of muscle, of breeze and waterfall, the chief credit rests with James
Watt, the inventor of the steam engine. Beside him stands George
Stephenson, who devised the locomotive which by abridging space has
lengthened life and added to its highest pleasures. Our volume closes by
narrating the competition which decided that Stephenson's "Rocket" was
much superior to its rivals, and thus opened a new chapter in the
history of mankind.
GEORGE ILES.
CONTENTS
FRANKLIN, BENJAMIN
LIGHTNING IDENTIFIED WITH ELECTRICITY
Franklin explains the action of the Leyden phial or jar.
Suggests lightning-rods. Sends a kite into the clouds during
a thunderstorm; through the kite-string obtains a spark
of lightning which throws into divergence the loose fibres
of the string, just as an ordinary electrical discharge
would do. 3
FARADAY, MICHAEL
PREPARING THE WAY FOR THE ELECTRIC DYNAMO AND MOTOR
Notices the inductive effect in one coil when the circuit in
a concentric coil is completed or broken. Notices similar
effects when a wire bearing a current approaches another
wire or recedes from it. Rotates a galvanometer needle by
an electric pulse. Induces currents in coils when the magnetism
is varied in their iron or steel cores. Observes the lines
of magnetic force as iron filings are magnetized. A magnetic
bar moved in and out of a coil of wire excites electricity
therein,--mechanical motion is converted into electricity.
Generates a current by spinning a copper plate in a horizontal
plane. 7
HENRY, JOSEPH
INVENTION OF THE ELECTRIC TELEGRAPH
Improves the electro-magnet of Sturgeon by insulating its
wire with silk thread, and by disposing the wire in several
coils instead of one. Experiments with a large electro-magnet
excited by nine distinct coils. Uses a battery so powerful
that electro-magnets are produced one hundred times more
energetic than those of Sturgeon. Arranges a telegraphic
circuit more than a mile long and at that distance sounds
a bell by means of an electro-magnet. 23
ILES, GEORGE
THE FIRST ATLANTIC CABLES
Forerunners at New York and Dover. Gutta-percha the indispensable
insulator. Wire is used to sheathe the cables. Cyrus W.
Field's project for an Atlantic cable. The first cable fails.
1858 so does the second cable 1865. A triumph of courage,
1866. The highway smoothed for successors. Lessons of the
cable. 37
BELL, ALEXANDER GRAHAM
THE INVENTION OF THE TELEPHONE
Indebted to his father's study of the vocal organs as they
form sounds. Examines the Helmholtz method for the analysis
and synthesis of vocal sounds. Suggests the electrical actuation
of tuning-forks and the electrical transmission of their
tones. Distinguishes intermittent, pulsatory and undulatory
currents. Devises as his first articulating telephone a harp
of steel rods thrown into vibration by electro-magnetism.
Exhibits optically the vibrations of sound, using a preparation
of a human ear: is struck by the efficiency of a slight
aural membrane. Attaches a bit of clock spring to a piece
of goldbeater's skin, speaks to it, an audible message is
received at a distant and similar device. This contrivance
improved is shown at the Centennial Exhibition, Philadelphia,
1876. At first the same kind of instrument transmitted and
delivered, a message; soon two distinct instruments were
invented for transmitting and for receiving. Extremely small
magnets suffice. A single blade of grass forms a telephonic
circuit. 57
DAM, H. J. W.
PHOTOGRAPHING THE UNSEEN
Roentgen indebted to the researches of Faraday, Clerk-Maxwell,
Hertz, Lodge and Lenard. The human optic nerve is affected
by a very small range in the waves that exist in the ether.
Beyond the visible spectrum of common light are vibrations
which have long been known as heat or as photographically
active. Crookes in a vacuous bulb produced soft light from
high tension electricity. Lenard found that rays from a
Crookes' tube passed through substances opaque to common
light. Roentgen extended these experiments and used the rays
photographically, taking pictures of the bones of the hand
through living flesh, and so on. 87
ILES, GEORGE
THE WIRELESS TELEGRAPH
What may follow upon electric induction. Telegraphy to a
moving train. The Preece induction method; its limits.
Marconi's system. His precursors, Hertz, Onesti, Branly
and Lodge. The coherer and the vertical wire form the essence
of the apparatus. Wireless telegraphy at sea. 109
ILES, GEORGE
ELECTRICITY, WHAT ITS MASTERY MEANS: WITH A REVIEW AND A PROSPECT
Electricity does all that fire ever did, does it better,
and performs uncounted services impossible to flame. Its
mastery means as great a forward stride as the subjugation
of fire. A minor invention or discovery simply adds to human
resources: a supreme conquest as of flame or electricity,
is a multiplier and lifts art and science to a new plane.
Growth is slow, flowering is rapid: progress at times is
so quick of pace as virtually to become a leap. The mastery
of electricity based on that of fire. Electricity vastly
wider of range than heat: it is energy in its most available
and desirable phase. The telegraph and the telephone contrasted
with the signal fire. Electricity as the servant of mechanic
and engineer. Household uses of the current. Electricity
as an agent of research now examines Nature in fresh aspects.
The investigator and the commercial exploiter render aid to
one another. Social benefits of electricity, in telegraphy, in
quick travel. The current should serve every city house. 125
RUMFORD, COUNT (BENJAMIN THOMPSON)
HEAT AND MOTION IDENTIFIED
Observes that in boring a cannon much heat is generated:
the longer the boring lasts, the more heat is produced. He
argues that since heat without limit may be thus produced
by motion, heat must be motion. 155
STEPHENSON, GEORGE
THE "ROCKET" LOCOMOTIVE AND ITS VICTORY
Shall it be a system of stationary engines or locomotives?
The two best practical engineers of the day are in favour
of stationary engines. A test of locomotives is, however,
proffered, and George Stephenson and his son, Robert, discuss
how they may best build an engine to win the first prize.
They adopt a steam blast to stimulate the draft of the furnace,
and raise steam quickly in a boiler having twenty-five small
fire-tubes of copper. The "Rocket" with a maximum speed of
twenty-nine miles an hour distances its rivals. With its
load of water its weight was but four and a quarter tons. 163
INVENTION AND DISCOVERY
FRANKLIN IDENTIFIES LIGHTNING WITH ELECTRICITY
[From Franklin's Works, edited in ten volumes by John Bigelow, Vol.
I, pages 276-281, copyright by G. P. Putnam's Sons, New York.]
Dr. Stuber, the author of the first continuation of Franklin's life,
gives this account of the electrical experiments of Franklin:--
"His observations he communicated, in a series of letters, to his friend
Collinson, the first of which is dated March 28, 1747. In these he shows
the power of points in drawing and throwing off the electrical matter,
which had hitherto escaped the notice of electricians. He also made the
grand discovery of a _plus_ and _minus_, or of a _positive_ and
_negative_ state of electricity. We give him the honour of this without
hesitation; although the English have claimed it for their countryman,
Dr. Watson. Watson's paper is dated January 21, 1748; Franklin's July
11, 1747, several months prior. Shortly after Franklin, from his
principles of the _plus_ and _minus_ state, explained in a satisfactory
manner the phenomena of the Leyden phial, first observed by Mr. Cuneus,
or by Professor Muschenbroeck, of Leyden, which had much perplexed
philosophers. He showed clearly that when charged the bottle contained
no more electricity than before, but that as much was taken from one
side as thrown on the other; and that to discharge it nothing was
necessary but to produce a communication between the two sides by which
the equilibrium might be restored, and that then no signs of electricity
would remain. He afterwards demonstrated by experiments that the
electricity did not reside in the coating as had been supposed, but in
the pores of the glass itself. After the phial was charged he removed
the coating, and found that upon applying a new coating the shock might
still be received. In the year 1749, he first suggested his idea of
explaining the phenomena of thunder gusts and of _aurora borealis_ upon
electric principles. He points out many particulars in which lightning
and electricity agree; and he adduces many facts, and reasonings from
facts, in support of his positions.
"In the same year he conceived the astonishingly bold and grand idea of
ascertaining the truth of his doctrine by actually drawing down the
lightning, by means of sharp pointed iron rods raised into the regions
of the clouds. Even in this uncertain state his passion to be useful to
mankind displayed itself in a powerful manner. Admitting the identity of
electricity and lightning, and knowing the power of points in repelling
bodies charged with electricity, and in conducting fires silently and
imperceptibly, he suggested the idea of securing houses, ships and the
like from being damaged by lightning, by erecting pointed rods that
should rise some feet above the most elevated part, and descend some
feet into the ground or water. The effect of these he concluded would be
either to prevent a stroke by repelling the cloud beyond the striking
distance or by drawing off the electrical fire which it contained; or,
if they could not effect this they would at least conduct the electrical
matter to the earth without any injury to the building.
"It was not until the summer of 1752 that he was enabled to complete his
grand and unparalleled discovery by experiment. The plan which he had
originally proposed was, to erect, on some high tower or elevated place,
a sentry-box from which should rise a pointed iron rod, insulated by
being fixed in a cake of resin. Electrified clouds passing over this
would, he conceived, impart to it a portion of their electricity which
would be rendered evident to the senses by sparks being emitted when a
key, the knuckle, or other conductor, was presented to it. Philadelphia
at this time afforded no opportunity of trying an experiment of this
kind. While Franklin was waiting for the erection of a spire, it
occurred to him that he might have more ready access to the region of
clouds by means of a common kite. He prepared one by fastening two cross
sticks to a silk handkerchief, which would not suffer so much from the
rain as paper. To the upright stick was affixed an iron point. The
string was, as usual, of hemp, except the lower end, which was silk.
Where the hempen string terminated, a key was fastened. With this
apparatus, on the appearance of a thundergust approaching, he went out
into the commons, accompanied by his son, to whom alone he communicated
his intentions, well knowing the ridicule which, too generally for the
interest of science, awaits unsuccessful experiments in philosophy. He
placed himself under a shed, to avoid the rain; his kite was raised, a
thunder-cloud passed over it, no sign of electricity appeared. He almost
despaired of success, when suddenly he observed the loose fibres of his
string to move towards an erect position. He now presented his knuckle
to the key and received a strong spark. How exquisite must his
sensations have been at this moment! On his experiment depended the fate
of his theory. If he succeeded, his name would rank high among those who
had improved science; if he failed, he must inevitably be subjected to
the derision of mankind, or, what is worse, their pity, as a
well-meaning man, but a weak, silly projector. The anxiety with which he
looked for the result of his experiment may easily be conceived. Doubts
and despair had begun to prevail, when the fact was ascertained, in so
clear a manner, that even the most incredulous could no longer withhold
their assent. Repeated sparks were drawn from the key, a phial was
charged, a shock given, and all the experiments made which are usually
performed with electricity."
FARADAY'S DISCOVERIES LEADING UP TO THE ELECTRIC DYNAMO AND MOTOR
[Michael Faraday was for many years Professor of Natural Philosophy
at the Royal Institution, London, where his researches did more to
subdue electricity to the service of man than those of any other
physicist who ever lived. "Faraday as a Discoverer," by Professor
John Tyndall (his successor) depicts a mind of the rarest ability
and a character of the utmost charm. This biography is published by
D. Appleton & Co., New York: the extracts which follow are from the
third chapter.]
In 1831 we have Faraday at the climax of his intellectual strength,
forty years of age, stored with knowledge and full of original power.
Through reading, lecturing, and experimenting, he had become thoroughly
familiar with electrical science: he saw where light was needed and
expansion possible. The phenomena of ordinary electric induction
belonged, as it were, to the alphabet of his knowledge: he knew that
under ordinary circumstances the presence of an electrified body was
sufficient to excite, by induction, an unelectrified body. He knew that
the wire which carried an electric current was an electrified body, and
still that all attempts had failed to make it excite in other wires a
state similar to its own.
What was the reason of this failure? Faraday never could work from the
experiments of others, however clearly described. He knew well that from
every experiment issues a kind of radiation, luminous, in different
degrees to different minds, and he hardly trusted himself to reason upon
an experiment that he had not seen. In the autumn of 1831 he began to
repeat the experiments with electric currents, which, up to that time,
had produced no positive result. And here, for the sake of younger
inquirers, if not for the sake of us all, it is worth while to dwell for
a moment on a power which Faraday possessed in an extraordinary degree.
He united vast strength with perfect flexibility. His momentum was that
of a river, which combines weight and directness with the ability to
yield to the flexures of its bed. The intentness of his vision in any
direction did not apparently diminish his power of perception in other
directions; and when he attacked a subject, expecting results, he had
the faculty of keeping his mind alert, so that results different from
those which he expected should not escape him through pre-occupation.
He began his experiments "on the induction of electric currents" by
composing a helix of two insulated wires, which were wound side by side
round the same wooden cylinder. One of these wires he connected with a
voltaic battery of ten cells, and the other with a sensitive
galvanometer. When connection with the battery was made, and while the
current flowed, no effect whatever was observed at the galvanometer.
But he never accepted an experimental result, until he had applied to
it the utmost power at his command. He raised his battery from ten cells
to one hundred and twenty cells, but without avail. The current flowed
calmly through the battery wire without producing, during its flow, any
sensible result upon the galvanometer.
"During its flow," and this was the time when an effect was
expected--but here Faraday's power of lateral vision, separating, as it
were from the line of expectation, came into play--he noticed that a
feeble movement of the needle always occurred at the moment when he made
contact with the battery; that the needle would afterwards return to its
former position and remain quietly there unaffected by the _flowing_
current. At the moment, however, when the circuit was interrupted the
needle again moved, and in a direction opposed to that observed on the
completion of the circuit.
This result, and others of a similar kind, led him to the conclusion
"that the battery current through the one wire did in reality induce a
similar current through the other; but that it continued for an instant
only, and partook more of the nature of the electric wave from a common
Leyden jar than of the current from a voltaic battery." The momentary
currents thus generated were called _induced currents_, while the
current which generated them was called the _inducing_ current. It was
immediately proved that the current generated at making the circuit was
always opposed in direction to its generator, while that developed on
the rupture of the circuit coincided in direction with the inducing
current. It appeared as if the current on its first rush through the
primary wire sought a purchase in the secondary one, and, by a kind of
kick, impelled backward through the latter an electric wave, which
subsided as soon as the primary current was fully established.
Faraday, for a time, believed that the secondary wire, though quiescent
when the primary current had been once established, was not in its
natural condition, its return to that condition being declared by the
current observed at breaking the circuit. He called this hypothetical
state of the wire the _electro-tonic state_: he afterwards abandoned
this hypothesis, but seemed to return to it in after life. The term
electro-tonic is also preserved by Professor Du Bois Reymond to express
a certain electric condition of the nerves, and Professor Clerk Maxwell
has ably defined and illustrated the hypothesis in the Tenth Volume of
the "Transactions of the Cambridge Philosophical Society."
The mere approach of a wire forming a closed curve to a second wire
through which a voltaic current flowed was then shown by Faraday to be
sufficient to arouse in the neutral wire an induced current, opposed in
direction to the inducing current; the withdrawal of the wire also
generated a current having the same direction as the inducing current;
those currents existed only during the time of approach or withdrawal,
and when neither the primary nor the secondary wire was in motion, no
matter how close their proximity might be, no induced current was
generated.
Faraday has been called a purely inductive philosopher. A great deal of
nonsense is, I fear, uttered in this land of England about induction and
deduction. Some profess to befriend the one, some the other, while the
real vocation of an investigator, like Faraday, consists in the
incessant marriage of both. He was at this time full of the theory of
Ampere, and it cannot be doubted that numbers of his experiments were
executed merely to test his deductions from that theory. Starting from
the discovery of Oersted, the celebrated French philosopher had shown
that all the phenomena of magnetism then known might be reduced to the
mutual attractions and repulsions of electric currents. Magnetism had
been produced from electricity, and Faraday, who all his life long
entertained a strong belief in such reciprocal actions, now attempted to
effect the evolution of electricity from magnetism. Round a welded iron
ring he placed two distinct coils of covered wire, causing the coils to
occupy opposite halves of the ring. Connecting the ends of one of the
coils with a galvanometer, he found that the moment the ring was
magnetized, by sending a current through _the other coil_, the
galvanometer needle whirled round four or five times in succession. The
action, as before, was that of a pulse, which vanished immediately. On
interrupting the current, a whirl of the needle in the opposite
direction occurred. It was only during the time of magnetization or
demagnetization that these effects were produced. The induced currents
declared a _change_ of condition only, and they vanished the moment the
act of magnetization or demagnetization was complete.
The effects obtained with the welded ring were also obtained with
straight bars of iron. Whether the bars were magnetized by the electric
current, or were excited by the contact of permanent steel magnets,
induced currents were always generated during the rise, and during the
subsidence of the magnetism. The use of iron was then abandoned, and the
same effects were obtained by merely thrusting a permanent steel magnet
into a coil of wire. A rush of electricity through the coil accompanied
the insertion of the magnet; an equal rush in the opposite direction
accompanied its withdrawal. The precision with which Faraday describes
these results, and the completeness with which he defined the boundaries
of his facts, are wonderful. The magnet, for example, must not be passed
quite through the coil, but only half through, for if passed wholly
through, the needle is stopped as by a blow, and then he shows how this
blow results from a reversal of the electric wave in the helix. He next
operated with the powerful permanent magnet of the Royal Society, and
obtained with it, in an exalted degree, all the foregoing phenomena.
And now he turned the light of these discoveries upon the darkest
physical phenomenon of that day. Arago had discovered in 1824, that a
disk of non-magnetic metal had the power of bringing a vibrating
magnetic needle suspended over it rapidly to rest; and that on causing
the disk to rotate the magnetic needle rotated along with it. When both
were quiescent, there was not the slightest measurable attraction or
repulsion exerted between the needle and the disk; still when in motion
the disk was competent to drag after it, not only a light needle, but a
heavy magnet. The question had been probed and investigated with
admirable skill by both Arago and Ampere, and Poisson had published a
theoretic memoir on the subject; but no cause could be assigned for so
extraordinary an action. It had also been examined in this country by
two celebrated men, Mr. Babbage and Sir John Herschel; but it still
remained a mystery. Faraday always recommended the suspension of
judgment in cases of doubt. "I have always admired," he says, "the
prudence and philosophical reserve shown by M. Arago in resisting the
temptations to give a theory of the effect he had discovered, so long as
he could not devise one which was perfect in its application, and in
refusing to assent to the imperfect theories of others." Now, however,
the time for theory had come. Faraday saw mentally the rotating disk,
under the operation of the magnet, flooded with his induced currents,
and from the known laws of interaction between currents and magnets he
hoped to deduce the motion observed by Arago. That hope he realized,
showing by actual experiment that when his disk rotated currents passed
through it, their position and direction being such as must, in
accordance with the established laws of electro-magnetic action, produce
the observed rotation.
Introducing the edge of his disk between the poles of the large
horseshoe magnet of the Royal Society, and connecting the axis and the
edge of the disk, each by a wire with a galvanometer, he obtained, when
the disk was turned round, a constant flow of electricity. The direction
of the current was determined by the direction of the motion, the
current being reversed when the rotation was reversed. He now states the
law which rules the production of currents in both disks and wires, and
in so doing uses, for the first time, a phrase which has since become
famous. When iron filings are scattered over a magnet, the particles of
iron arrange themselves in certain determined lines called magnetic
curves. In 1831, Faraday for the first time called these curves "lines
of magnetic force;" and he showed that to produce induced currents
neither approach to nor withdrawal from a magnetic source, or centre, or
pole, was essential, but that it was only necessary to cut appropriately
the lines of magnetic force. Faraday's first paper on Magneto-electric
Induction, which I have here endeavoured to condense, was read before
the Royal Society on the 24th of November, 1831.
On January 12, 1832, he communicated to the Royal Society a second paper
on "Terrestrial Magneto-electric Induction," which was chosen as the
Bakerian Lecture for the year. He placed a bar of iron in a coil of
wire, and lifting the bar into the direction of the dipping needle, he
excited by this action a current in the coil. On reversing the bar, a
current in the opposite direction rushed through the wire. The same
effect was produced, when, on holding the helix in the line of dip, a
bar of iron was thrust into it. Here, however, the earth acted on the
coil through the intermediation of the bar of iron. He abandoned the bar
and simply set a copper-plate spinning in a horizontal plane; he knew
that the earth's lines of magnetic force then crossed the plate at an
angle of about 70 deg.. When the plate spun round, the lines of force were
intersected and induced currents generated, which produced their proper
effect when carried from the plate to the galvanometer. "When the plate
was in the magnetic meridian, or in any other plane coinciding with the
magnetic dip, then its rotation produced no effect upon the
galvanometer."
At the suggestion of a mind fruitful in suggestions of a profound and
philosophic character--I mean that of Sir John Herschel--Mr. Barlow, of
Woolwich, had experimented with a rotating iron shell. Mr. Christie had
also performed an elaborate series of experiments on a rotating iron
disk. Both of them had found that when in rotation the body exercised a
peculiar action upon the magnetic needle, deflecting it in a manner
which was not observed during quiescence; but neither of them was aware
at the time of the agent which produced this extraordinary deflection.
They ascribed it to some change in the magnetism of the iron shell and
disk.
But Faraday at once saw that his induced currents must come into play
here, and he immediately obtained them from an iron disk. With a hollow
brass ball, moreover, he produced the effects obtained by Mr. Barlow.
Iron was in no way necessary: the only condition of success was that the
rotating body should be of a character to admit of the formation of
currents in its substance: it must, in other words, be a conductor of
electricity. The higher the conducting power the more copious were the
currents. He now passes from his little brass globe to the globe of the
earth. He plays like a magician with the earth's magnetism. He sees the
invisible lines along which its magnetic action is exerted and sweeping
his wand across these lines evokes this new power. Placing a simple loop
of wire round a magnetic needle he bends its upper portion to the west:
the north pole of the needle immediately swerves to the east: he bends
his loop to the east, and the north poles moves to the west. Suspending
a common bar magnet in a vertical position, he causes it to spin round
its own axis. Its pole being connected with one end of a galvanometer
wire, and its equator with the other end, electricity rushes round the
galvanometer from the rotating magnet. He remarks upon the "_singular
independence_" of the magnetism and the body of the magnet which carries
it. The steel behaves as if it were isolated from its own magnetism.
And then his thoughts suddenly widen, and he asks himself whether the
rotating earth does not generate induced currents as it turns round its
axis from west to east. In his experiment with the twirling magnet the
galvanometer wire remained at rest; one portion of the circuit was in
motion _relatively_ to _another portion_. But in the case of the
twirling planet the galvanometer wire would necessarily be carried along
with the earth; there would be no relative motion. What must be the
consequence? Take the case of a telegraph wire with its two terminal
plates dipped into the earth, and suppose the wire to lie in the
magnetic meridian. The ground underneath the wire is influenced like the
wire itself by the earth's rotation; if a current from south to north be
generated in the wire, a similar current from south to north would be
generated in the earth under the wire; these currents would run against
the same terminal plates, and thus neutralize each other.
This inference appears inevitable, but his profound vision perceived its
possible invalidity. He saw that it was at least possible that the
difference of conducting power between the earth and the wire might
give one an advantage over the other, and that thus a residual or
differential current might be obtained. He combined wires of different
materials, and caused them to act in opposition to each other, but found
the combination ineffectual. The more copious flow in the better
conductor was exactly counterbalanced by the resistance of the worst.
Still, though experiment was thus emphatic, he would clear his mind of
all discomfort by operating on the earth itself. He went to the round
lake near Kensington Palace, and stretched four hundred and eighty feet
of copper wire, north and south, over the lake, causing plates soldered
to the wire at its ends to dip into the water. The copper wire was
severed at the middle, and the severed ends connected with a
galvanometer. No effect whatever was observed. But though quiescent
water gave no effect, moving water might. He therefore worked at London
Bridge for three days during the ebb and flow of the tide, but without
any satisfactory result. Still he urges, "Theoretically it seems a
necessary consequence, that where water is flowing there electric
currents should be formed. If a line be imagined passing from Dover to
Calais through the sea, and returning through the land, beneath the
water, to Dover, it traces out a circuit of conducting matter one part
of which, when the water moves up or down the channel, is cutting the
magnetic curves of the earth, while the other is relatively at rest....
There is every reason to believe that currents do run in the general
direction of the circuit described, either one way or the other,
according as the passage of the waters is up or down the channel." This
was written before the submarine cable was thought of, and he once
informed me that actual observation upon that cable had been found to be
in accordance with his theoretic deduction.
Three years subsequent to the publication of these researches, that is
to say on January 29, 1835, Faraday read before the Royal Society a
paper "On the influence by induction of an electric current upon
itself." A shock and spark of a peculiar character had been observed by
a young man named William Jenkin, who must have been a youth of some
scientific promise, but who, as Faraday once informed me, was dissuaded
by his own father from having anything to do with science. The
investigation of the fact noticed by Mr. Jenkin led Faraday to the
discovery of the _extra current_, or the current _induced in the primary
wire itself_ at the moments of making and breaking contact, the
phenomena of which he described and illustrated in the beautiful and
exhaustive paper referred to.
Seven and thirty years have passed since the discovery of
magneto-electricity; but, if we except the _extra current_, until quite
recently nothing of moment was added to the subject. Faraday entertained
the opinion that the discoverer of a great law or principle had a right
to the "spoils"--this was his term--arising from its illustration; and
guided by the principle he had discovered, his wonderful mind, aided by
his wonderful ten fingers, overran in a single autumn this vast domain,
and hardly left behind him the shred of a fact to be gathered by his
successors.
And here the question may arise in some minds, What is the use of it
all? The answer is, that if man's intellectual nature thirsts for
knowledge then knowledge is useful because it satisfies this thirst. If
you demand practical ends, you must, I think, expand your definition of
the term practical, and make it include all that elevates and enlightens
the intellect, as well as all that ministers to the bodily health and
comfort of men. Still, if needed, an answer of another kind might be
given to the question "what is its use?" As far as electricity has been
applied for medical purposes, it has been almost exclusively Faraday's
electricity. You have noticed those lines of wire which cross the
streets of London. It is Faraday's currents that speed from place to
place through these wires. Approaching the point of Dungeness, the
mariner sees an unusually brilliant light, and from the noble lighthouse
of La Heve the same light flashes across the sea. These are Faraday's
sparks exalted by suitable machinery to sun-like splendour. At the
present moment the Board of Trade and the Brethren of the Trinity House,
as well as the Commissioners of Northern Lights, are contemplating the
introduction of the Magneto-electric Light at numerous points upon our
coasts; and future generations will be able to refer to those guiding
stars in answer to the question, what has been the practical use of the
labours of Faraday? But I would again emphatically say, that his work
needs no justification, and that if he had allowed his vision to be
disturbed by considerations regarding the practical use of his
discoveries, those discoveries would never have been made by him. "I
have rather," he writes in 1831, "been desirous of discovering new facts
and new relations dependent on magneto-electric induction, than of
exalting the force of those already obtained; being assured that the
latter would find their full development hereafter."
In 1817, when lecturing before a private society in London on the
element chlorine, Faraday thus expresses himself with reference to this
question of utility. "Before leaving this subject, I will point out the
history of this substance as an answer to those who are in the habit of
saying to every new fact, 'What is its use?' Dr. Franklin says to such,
'What is the use of an infant?' The answer of the experimentalist is,
'Endeavour to make it useful.' When Scheele discovered this substance,
it appeared to have no use; it was in its infancy and useless state, but
having grown up to maturity, witness its powers, and see what endeavours
to make it useful have done."
PROFESSOR JOSEPH HENRY'S INVENTION OF THE ELECTRIC TELEGRAPH
[In 1855 the Regents of the Smithsonian Institution, Washington, D.
C., at the instance of their secretary, Professor Joseph Henry,
took evidence with respect to his claims as inventor of the
electric telegraph. The essential paragraphs of Professor Henry's
statement are taken from the Proceedings of the Board of Regents of
the Smithsonian Institution, Washington, 1857.]
There are several forms of the electric telegraph; first, that in which
frictional electricity has been proposed to produce sparks and motion of
pith balls at a distance.
Second, that in which galvanism has been employed to produce signals by
means of bubbles of gas from the decomposition of water.
Third, that in which electro-magnetism is the motive power to produce
motion at a distance; and again, of the latter there are two kinds of
telegraphs, those in which the intelligence is indicated by the motion
of a magnetic needle, and those in which sounds and permanent signs are
made by the attraction of an electro-magnet. The latter is the class to
which Mr. Morse's invention belongs. The following is a brief exposition
of the several steps which led to this form of the telegraph.
The first essential fact which rendered the electro-magnetic telegraph
possible was discovered by Oersted, in the winter of 1819-'20. It is
illustrated by figure 1, in which the magnetic needle is deflected by
the action of a current of galvanism transmitted through the wire A B.
[Illustration: Fig. 1]
The second fact of importance, discovered in 1820, by Arago and Davy, is
illustrated in Fig. 2. It consists in this, that while a current of
galvanism is passing through a copper wire A B, it is magnetic, it
attracts iron filings and not those of copper or brass, and is capable
of developing magnetism in soft iron.
[Illustration: Fig. 2]
The next important discovery, also made in 1820, by Ampere, was that two
wires through which galvanic currents are passing in the same direction
attract, and in the opposite direction, repel, each other. On this fact
Ampere founded his celebrated theory, that magnetism consists merely in
the attraction of electrical currents revolving at right angles to the
line joining the two poles of the magnet. The magnetization of a bar of
steel or iron, according to this theory consists in establishing within
the metal by induction a series of electrical currents, all revolving in
the same direction at right angles to the axis or length of the bar.
[Illustration: Fig. 3]
It was this theory which led Arago, as he states, to adopt the method of
magnetizing sewing needles and pieces of steel wire, shown in Fig. 3.
This method consists in transmitting a current of electricity through a
helix surrounding the needle or wire to be magnetised. For the purpose
of insulation the needle was enclosed in a glass tube, and the several
turns of the helix were at a distance from each other to insure the
passage of electricity through the whole length of the wire, or, in
other words, to prevent it from seeking a shorter passage by cutting
across from one spire to another. The helix employed by Arago obviously
approximates the arrangement required by the theory of Ampere, in order
to develop by induction the magnetism of the iron. By an attentive
perusal of the original account of the experiments of Arago, it will be
seen that, properly speaking, he made no electro-magnet, as has been
asserted by Morse and others; his experiments were confined to the
magnetism of iron filings, to sewing needles and pieces of steel wire of
the diameter of a millimetre, or of about the thickness of a small
knitting needle.
[Illustration: Fig. 4]
Mr. Sturgeon, in 1825, made an important step in advance of the
experiments of Arago, and produced what is properly known as the
electro-magnet. He bent a piece of iron _wire_ into the form of a
horseshoe, covered it with varnish to insulate it, and surrounded it
with a helix, of which the spires were at a distance. When a current of
galvanism was passed through the helix from a small battery of a single
cup the iron wire became magnetic, and continued so during the passage
of the current. When the current was interrupted the magnetism
disappeared, and thus was produced the first temporary soft iron
magnet.
The electro-magnet of Sturgeon is shown in Fig. 4. By comparing Figs. 3
and 4 it will be seen that the helix employed by Sturgeon was of the
same kind as that used by Arago; instead however, of a straight steel
wire inclosed in a tube of glass, the former employed a bent wire of
soft iron. The difference in the arrangement at first sight might appear
to be small, but the difference in the results produced was important,
since the temporary magnetism developed in the arrangement of Sturgeon
was sufficient to support a weight of several pounds, and an instrument
was thus produced of value in future research.
[Illustration: Fig. 5]
The next improvement was made by myself. After reading an account of the
galvanometer of Schweigger, the idea occurred to me that a much nearer
approximation to the requirements of the theory of Ampere could be
attained by insulating the conducting wire itself, instead of the rod to
be magnetized, and by covering the whole surface of the iron with a
series of coils in close contact. This was effected by insulating a long
wire with silk thread, and winding this around the rod of iron in close
coils from one end to the other. The same principle was extended by
employing a still longer insulated wire, and winding several strata of
this over the first, care being taken to insure the insulation between
each stratum by a covering of silk ribbon. By this arrangement the rod
was surrounded by a compound helix formed of a long wire of many coils,
instead of a single helix of a few coils, (Fig. 5).
In the arrangement of Arago and Sturgeon the several turns of wire were
not precisely at right angles to the axis of the rod, as they should be,
to produce the effect required by the theory, but slightly oblique, and
therefore each tended to develop a separate magnetism not coincident
with the axis of the bar. But in winding the wire over itself, the
obliquity of the several turns compensated each other, and the resultant
action was at right angles to the bar. The arrangement then introduced
by myself was superior to those of Arago and Sturgeon, first in the
greater multiplicity of turns of wire, and second in the better
application of these turns to the development of magnetism. The power of
the instrument with the same amount of galvanic force, was by this
arrangement several times increased.
The maximum effect, however, with this arrangement and a single battery
was not yet obtained. After a certain length of wire had been coiled
upon the iron, the power diminished with a further increase of the
number of turns. This was due to the increased resistance which the
longer wire offered to the conduction of electricity. Two methods of
improvement therefore suggested themselves. The first consisted, not in
increasing the length of the coil, but in using a number of separate
coils on the same piece of iron. By this arrangement the resistance to
the conduction of the electricity was diminished and a greater quantity
made to circulate around the iron from the same battery. The second
method of producing a similar result consisted in increasing the number
of elements of the battery, or, in other words, the projectile force of
the electricity, which enabled it to pass through an increased number of
turns of wire, and thus, by increasing the length of the wire, to
develop the maximum power of the iron.
[Illustration: Fig. 6]
To test these principles on a larger scale, the experimental magnet was
constructed, which is shown in Fig. 6. In this a number of compound
helices were placed on the same bar, their ends left projecting, and so
numbered that they could be all united into one long helix, or variously
combined in sets of lesser length.
From a series of experiments with this and other magnets it was proved
that, in order to produce the greatest amount of magnetism from a
battery of a single cup, a number of helices is required; but when a
compound battery is used, then one long wire must be employed, making
many turns around the iron, the length of wire and consequently the
number of turns being commensurate with the projectile power of the
battery.
In describing the results of my experiments, the terms _intensity_ and
_quantity_ magnets were introduced to avoid circumlocution, and were
intended to be used merely in a technical sense. By the _intensity_
magnet I designated a piece of soft iron, so surrounded with wire that
its magnetic power could be called into operation by an _intensity_
battery, and by a _quantity_ magnet, a piece of iron so surrounded by a
number of separate coils, that its magnetism could be fully developed by
a _quantity_ battery.
I was the first to point out this connection of the two kinds of the
battery with the two forms of the magnet, in my paper in _Silliman's
Journal_, January, 1831, and clearly to state that when magnetism was to
be developed by means of a compound battery, one long coil was to be
employed, and when the maximum effect was to be produced by a single
battery, a number of single strands were to be used.
These steps in the advance of electro-magnetism, though small, were such
as to interest and astonish the scientific world. With the same battery
used by Mr. Sturgeon, at least a hundred times more magnetism was
produced than could have been obtained by his experiment. The
developments were considered at the time of much importance in a
scientific point of view, and they subsequently furnished the means by
which magneto-electricity, the phenomena of dia-magnetism, and the
magnetic effects on polarized light were discovered. They gave rise to
the various forms of electro-magnetic machines which have since
exercised the ingenuity of inventors in every part of the world, and
were of immediate applicability in the introduction of the magnet to
telegraphic purposes. Neither the electro-magnet of Sturgeon nor any
electro-magnet ever made previous to my investigations was applicable to
transmitting power to a distance.