A History of Science - v.3 (Williams)

practical instrument, it can hardly be called one that puts electricity to practical use, but simply acts as a means of warding off the evil effects of a natural manifestation of electricity. The invention, however, had all the effects of a mechanism which turned electricity to practical account. But with the advent of the new

kind of electricity the age of practical application began.

DAVY AND ELECTRIC LIGHT

Volta's announcement of his pile was scarcely two months old when two Englishmen, Messrs. Nicholson

and Carlisle, made the discovery that the current from the galvanic battery had a decided effect upon certain chemicals, among other things decomposing water

into its elements, hydrogen and oxygen. On May 7, 1800, these investigators arranged the ends of two

brass wires connected with the poles of a voltaic pile, composed of alternate silver and zinc plates, so that the current coming from the pile was discharged

through a small quantity of "New River water." "A fine stream of minute bubbles immediately began

to flow from the point of the lower wire in the tube which communicated with the silver," wrote Nicholson, "and the opposite point of the upper wire became tarnished, first deep orange and then black. . . ." The product of gas during two hours and a half was two-

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This demonstration was the beginning of the very important science of electro-chemistry.

The importance of this discovery was at once recognized by Sir Humphry Davy, who began experimenting immediately in this new field. He constructed a

series of batteries in various combinations, with which he attacked the "fixed alkalies," the composition of which was then unknown. Very shortly he was able

to decompose potash into bright metallic globules, resembling quicksilver. This new substance he named "potassium." Then in rapid succession the elementary substances sodium, calcium, strontium, and magnesium were isolated.

It was soon discovered, also, that the new electricity, like the old, possessed heating power under certain conditions, even to the fusing of pieces of wire. This observation was probably first made by Frommsdorff,

but it was elaborated by Davy, who constructed a battery of two thousand cells with which he produced

a bright light from points of carbon--the prototype of the modern arc lamp. He made this demonstration

before the members of the Royal Institution in 1810.

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But the practical utility of such a light for illuminating purposes was still a thing of the future. The expense

of constructing and maintaining such an elaborate

battery, and the rapid internal destruction of its plates, together with the constant polarization, rendered its

use in practical illumination out of the question. It was not until another method of generating electricity was discovered that Davy's demonstration could be turned to practical account.

In Davy's own account of his experiment he says:

"When pieces of charcoal about an inch long and one-sixth of an inch in diameter were brought near each other (within the thirtieth or fortieth of an inch), a bright spark was produced, and more than half the volume of the charcoal became ignited to whiteness;

and, by withdrawing the points from each other, a constant discharge took place through the heated air, in a

space equal to at least four inches, producing a most brilliant ascending arch of light, broad and conical in form in the middle. When any substance was introduced into this arch, it instantly became ignited;

platina melted as readily in it as wax in a common candle; quartz, the sapphire, magnesia, lime, all entered

into fusion; fragments of diamond and points of charcoal and plumbago seemed to evaporate in it, even

when the connection was made in the receiver of an

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air-pump; but there was no evidence of their having previously undergone fusion. When the communication between the points positively and negatively electrified was made in the air rarefied in the receiver of the air-pump, the distance at which the discharge took

place increased as the exhaustion was made; and when the atmosphere in the vessel supported only one-

fourth of an inch of mercury in the barometrical gauge, the sparks passed through a space of nearly half an inch; and, by withdrawing the points from each other, the discharge was made through six or seven inches, producing a most brilliant coruscation of purple light; the charcoal became intensely ignited, and some platina wire attached to it fused with brilliant scintillations and fell in large globules upon the plate of the pump. All the phenomena of chemical decomposition were produced with intense rapidity by this combination."[1]

But this experiment demonstrated another thing

besides the possibility of producing electric light and chemical decomposition, this being the heating power capable of being produced by the electric current.

Thus Davy's experiment of fusing substances laid the foundation of the modern electric furnaces, which are of paramount importance in several great commercial industries.

While some of the results obtained with Davy's batteries were practically as satisfactory as could be

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in electricity were rendered comparatively

easy. In the mean while, however, another great discovery was made.

ELECTRICITY AND MAGNETISM

For many years there had been a growing suspicion, amounting in many instances to belief in the close relationship existing between electricity and magnetism. Before the winter of 1815, however, it was a belief

that was surmised but not demonstrated. But in that year it occurred to Jean Christian Oersted, of Denmark,

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to pass a current of electricity through a wire

held parallel with, but not quite touching, a suspended magnetic needle. The needle was instantly deflected

and swung out of its position.

"The first experiments in connection with the subject which I am undertaking to explain," wrote Oersted, "were made during the course of lectures which

I held last winter on electricity and magnetism. From those experiments it appeared that the magnetic needle could be moved from its position by means of a galvanic battery--one with a closed galvanic circuit.

Since, however, those experiments were made with an apparatus of small power, I undertook to repeat and increase them with a large galvanic battery.

"Let us suppose that the two opposite ends of the galvanic apparatus are joined by a metal wire. This

I shall always call the conductor for the sake of brevity. Place a rectilinear piece of this conductor in a horizontal position over an ordinary magnetic needle so that

it is parallel to it. The magnetic needle will be set in motion and will deviate towards the west under that

part of the conductor which comes from the negative pole of the galvanic battery. If the wire is not more than four-fifths of an inch distant from the middle of

this needle, this deviation will be about forty-five degrees. At a greater distance the angle of deviation

becomes less. Moreover, the deviation varies according

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to the strength of the battery. The conductor can

be moved towards the east or west, so long as it remains parallel to the needle, without producing any

other result than to make the deviation smaller.

"The conductor can consist of several combined

wires or metal coils. The nature of the metal does not alter the result except, perhaps, to make it greater or less. We have used wires of platinum, gold, silver, brass, and iron, and coils of lead, tin, and quicksilver with the same result. If the conductor is interrupted

by water, all effect is not cut off, unless the stretch of water is several inches long.

"The conductor works on the magnetic needle

through glass, metals, wood, water, and resin, through clay vessels and through stone, for when we placed a

glass plate, a metal plate, or a board between the conductor and the needle the effect was not cut off; even

the three together seemed hardly to weaken the effect, and the same was the case with an earthen vessel, even

when it was full of water. Our experiments also demonstrated that the said effects were not altered when

we used a magnetic needle which was in a brass case full of water.

"When the conductor is placed in a horizontal plane

under the magnetic needle all the effects we have described

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take place in precisely the same way, but in

the opposite direction to what took place when the conductor was in a horizontal plane above the needle.

"If the conductor is moved in a horizontal plane so that it gradually makes ever-increasing angles with the magnetic meridian, the deviation of the magnetic

needle from the magnetic meridian is increased when the wire is turned towards the place of the needle; it decreases, on the other hand, when it is turned away from that place.

"A needle of brass which is hung in the same way as

the magnetic needle is not set in motion by the influence of the conductor. A needle of glass or rubber likewise remains static under similar experiments. Hence

the electrical conductor affects only the magnetic parts of a substance. That the electrical current is

not confined to the conducting wire, but is comparatively widely diffused in the surrounding space, is

sufficiently demonstrated from the foregoing observations."[2]

The effect of Oersted's demonstration is almost incomprehensible. By it was shown the close relationship between magnetism and electricity. It showed

the way to the establishment of the science of electrodynamics; although it was by the French savant

Andre Marie Ampere (1775-1836) that the science was

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actually created, and this within the space of one week after hearing of Oersted's experiment in deflecting the needle. Ampere first received the news of Oersted's experiment on September 11, 1820, and on the 18th

of the same month he announced to the Academy the fundamental principles of the science of electro-dynamics-- seven days of rapid progress perhaps unequalled

in the history of science.

Ampere's distinguished countryman, Arago, a few months later, gave the finishing touches to Oersted's

and Ampere's discoveries, by demonstrating conclusively that electricity not only influenced a magnet,

but actually produced magnetism under proper circumstances --a complemental fact most essential in

practical mechanics

Some four years after Arago's discovery, Sturgeon made the first "electro-magnet" by winding a soft

iron core with wire through which a current of electricity was passed. This study of electro-magnets

was taken up by Professor Joseph Henry, of Albany, New York, who succeeded in making magnets of enormous lifting power by winding the iron core with several coils of wire. One of these magnets, excited by

a single galvanic cell of less than half a square foot of surface, and containing only half a pint of dilute acids, sustained a weight of six hundred and fifty

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pounds.

Thus by Oersted's great discovery of the intimate relationship of magnetism and electricity, with further elaborations and discoveries by Ampere, Volta, and Henry, and with the invention of Daniell's cell, the way was laid for putting electricity to practical use. Soon followed the invention and perfection of the electro-magnetic telegraph and a host of other but little less important devices.

FARADAY AND ELECTRO-MAGNETIC INDUCTION

With these great discoveries and inventions at hand, electricity became no longer a toy or a "plaything for philosophers," but of enormous and growing importance commercially. Still, electricity generated by

chemical action, even in a very perfect cell, was both feeble and expensive, and, withal, only applicable in a comparatively limited field. Another important scientific discovery was necessary before such things as

electric traction and electric lighting on a large scale were to become possible; but that discovery was soon made by Sir Michael Faraday.

Faraday, the son of a blacksmith and a bookbinder by trade, had interested Sir Humphry Davy by his

admirable notes on four of Davy's lectures, which he

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