VI.

NOTES ON RECENT PROGRESS IN APPLIED

SCIENCE.

THE science of to-day, like everything else, material or intellectual, is the child of the past, and our latest discoveries owe their very being to the old and almost forgotten labors and achievements of the earlier ages; just as the earth of to-day owes its present condition and capacity for sustaining the complex existence of modern civilization, with all its refinement and beauty, to the long history of change and development beginning with the original chaos and passing through the periods of monstrous vegetable and animal life, of tree-ferns and of saurians, and the other eras of geologic change, and coming down through the dark ages of barbarous human development to our own time.

As one of our poets very beautifully expressed this idea :

What fiery fields of Chaos must be won,

What battling Titans rear themselves a tomb,
What births and resurrections greet the sun,
Before the rose can bloom!

And of some wonder-blossom yet we dream
Whereof the time that is infolds the seed,-
Some flower of light, to which the rose shall seem

A fair and fragile weed.

In consequence of this, it is hardly possible to describe any new development without large reference to the old foundation on which it is built, or the old material out of which it is formed.

Progress in Electric Science.

Thus the most remarkable and striking developments of late have been in subjects involving the principles of electric induction

first brought to light by Faraday in 1831. The Bell telephone and the electric light of to-day are the direct applications of the principle first announced by Faraday in 1831.

A few words as to this principle and its connection with these. applications will, then, come in good place, not only to make clear the latest developments in these directions, but also to prepare us for the next steps which may perhaps be taken before this present writing can reach the eye of its readers; for so rapid is this progress that it even outstrips the marvelous rapidity of the compositor and the power-press.

In brief, then, this important principle is this: Whenever a conductor, such for example as a copper wire, is moved near a magnet so as to cut those directions in which iron filings arrange themselves about the poles of a magnet, and which are often called "lines of magnetic force "-whenever, we say, a conductor cuts these lines, a current of electricity is caused to flow through such a conductor. It is evidently immaterial whether the conductor is moved across the lines of force of a magnet at rest; or, the conductor being at rest, the magnet with its lines of force is moved in reference to the conductor; or, lastly, whether, both conductor and magnet being at rest, the lines of force are caused to move in reference to both magnet and conductor. In either case lines of force will be cut by a conductor, and a current will be developed as long as the cutting or relative motion between the conductor and lines of force continues. It is this simple principle which is at the foundation of all the electric-light machines and most of the telephones now in use.

Coils of wire are made to revolve rapidly near to powerful magnets, and by this means electric currents are generated which are then used, in one way or another, for the production of light. It must not, however, be forgotten that here, as everywhere else, the great doctrine of "conservation of energy" is maintained-that doctrine which found a prophetic expression in the proverb, one of whose homely forms was, "You can not have your cake and eat it too." In other words, and with special application to this case, you can not have an electric current and also the power required to generate it.

When the current begins to flow in the conductors or wire coils, it develops in them a powerful attraction for the magnets near which they are moved, and to continue the motion a great force must be continuously applied and expended.

Thus it comes about, that to produce electric currents with these

magneto-electric machines, as they are called, a large amount of mechanical force must be applied, as for example the power of a steam-engine; and thus we get the electric current only by giving for it so much as its equivalent, of energy, which is derived from the fuel consumed in the furnace of the steam-boiler.

We are, therefore, getting the electric current at the expense of the coal consumed (making no allowance for losses), and, though this is very much less expensive than any method before known of obtaining an electric current, we would make a serious mistake if we forgot or neglected to include it in making any calculations as to the practicability and economy of electricity as a source of light or other effect.

Bearing this in mind, however, we find that recent improvements in the structure of magneto-electric machines have so developed their efficiency, that in the best forms as much as eighty per cent. of the energy applied to them is converted into electric current.

In other words, for every hundred horse-power expended in turning the machines, eighty horse-power is converted into electric force, and only twenty horse-power is wasted or lost in doing useless work, such as heating the machine itself.

Compared with other machines, this is a very wonderful performance. Our best steam-engines almost exactly reverse these figures; that is to say, our best steam-engines give us an available power of about twenty per cent. of the energy given out by the fuel burned in their furnaces, and waste eighty per cent. in heat thrown up the chimney and otherwise dissipated.

While, therefore, there is an immense margin for improvement in the economy and efficiency of our steam-engines, the magnetoelectric machines have nearly reached the maximum possible of effectiveness, and any one who proposes to double their performance in this respect, either does not know what the good ones now accomplish, or does not understand the subject.

In applying the electric currents which these magneto-electric machines develop to the production of light, two principal means have been employed: first, the electric arc; second, the incandescence of a heated conductor.

The electric arc was first shown by Sir Humphry Davy in 1808, and is produced by interrupting a powerful electric current between two points of carbon. To accomplish this we have two pieces of carbon in contact with each other, and so connected with a galvanic battery or magneto-electric machine that the current flows

through them; then, on separating the pieces of carbon gradually from each other, the electric current springs across the gap, carrying with it particles of carbon and carbon vapor, which make a flying bridge by which it continues to travel across.

In thus tearing off particles from one side and hurling them against the other, intense heat and light vibrations are occasioned in both poles or points, and in the flying fragments, and this is what constitutes the electric arc.

Such an arc may develop a light equal to that of five hundred or of twenty thousand candles, and is so far, much the most efficient and economical means by which electric force can be converted into light.

The best results as yet obtained show that for each horse-power expended in turning the magneto-electric machine a light equal to that of two thousand candles (or one hundred and twenty-five gasburners) can be obtained.

A first-rate engine should not need more than three pounds of coal per horse-power per hour, so that in every case where a light of some hundreds of gas-burners in one place is required the light of the electric arc would be very economical. The difficulties which at present limit its use in this connection are the result of its great intensity and more or less unsteadiness, and the inconvenience of having a steam-engine in certain localities. Multitudes of ingenious inventors are busy devising electric lamps to overcome the former of these difficulties, and without doubt the electric-arc light will daily extend its field of illumination among our factories, workshops, and public buildings generally.

Electric incandescence, as a source of light, made its appearance at about the same time and in the same place as the electric arc, but it was first reduced to a practical shape about twenty years ago by M. de Changy in Paris, and by Mr. Moses G. Farmer in Salem, Massachusetts. Both of these gentlemen seem to have developed electric lamps operating by the incandescence of a metallic wire, and having an efficient automatic regulator by which their constancy of action was secured; but the great cost of electricity, produced at that time by the galvanic battery, caused the abandonment of all efforts to make any practical use of such apparatus. Now, however, that a relatively cheap source of electricity is found in the magneto-electric machine, these old plans have been revived, and we find in Mr. Edison's English patents a redevelopment of the same thing.

They all operate on the fact that when a powerful current of VOL. CXXVIII. NO. 270.

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electricity traverses an insufficient conductor, as a wire or narrow strip of platinum, for example, the same is intensely heated, and so becomes luminous. Coils of wire, strips of platinum, or the like, are therefore so arranged that a current shall pass through them, and so make them luminously hot or incandescent. As this incandescence is greatest near the fusing-point of these substances, and their fusion would of course interrupt the action, various ingenious contrivances are adopted by which the current is automatically shut off or diverted if it approaches too near to this disastrous result. Thus, for example, the strip of incandescent metal itself so operates a lever that as soon as its expansion reaches a certain degree it closes a circuit, which diverts part of the current into another conductor.

There are a multitude of these contrivances, and almost every day sees new ones added to the list, but so far they have all been very elaborate, often complicated, and, as a rule, expensive instru

ments.

Another plan is to use, in place of a metal which may be fused, a thin rod of carbon, which can not be fused, and whose tendency to burn is overcome by inclosing it in a glass vessel filled with some gas which can not combine with it, nitrogen for example. Lamps of this nature have been largely experimented with, and inventors are still laboring upon them, but as yet the success obtained is not such as to warrant their practical introduction into actual use.

In all plans of obtaining light by electric incandescence so far published, the cost of the light has been many times greater than with the electric arc.

On the other hand, by incandescence, lights of moderate power, equal for example to one or two gas-burners, can be produced, and this would be of course a property of essential importance in any general use of electricity for domestic lighting.

It is on these subjects that several of the most ingenious minds of the day are now working, and what we have above stated not only gives the present state of the problem, but will prepare the reader to comprehend the new developments as they appear.

The next application of Faraday's discovery of magneto-induction is found in the Bell telephone. In this instrument a series of electric currents is developed by the movements of a thin plate of iron in front of a steel magnet, around whose end a wire is coiled. As the thin iron plate vibrates to the impulse received from the voice of one speaking near it, the lines of force about the magnet are caused to move, and so cut across the coils of wire, and conse