Part 3

I will measure the wave lengths of light thus: I walk away to a considerable distance, and look at the candle and marks. I see a set of spectrums. The first white line is exactly behind the candle. I want the first spectrum to the right of that white line to fall exactly on the other white line, which is ten inches from the first. As I walk away from it, I see it is now very near it; it is now on it. Now the distance from my eye is to be measured, and the problem is again to reduce feet to inches. The distance from the spectrum of the flame to my eye is thirty-four feet nine inches. Mr. President, how many inches is that? Four hundred and seventeen inches, in round numbers 420 inches. Then we have the proportion, as 420 is to 10 so is the length from bar to bar of the grating to the wave length of sodium light--that is to say, as forty-two is to one. The distance from bar to bar is the four-hundredth of a centimeter; therefore the 42d part of the four-hundredth of a centimeter is the required wave length, or the 16,800th of a centimeter is the wave length according to our simple, and easy, and hasty experiment. The true wave length of sodium light, according to the most accurate measurement, is about a 17,000th of a centimeter, which differs by scarcely more than one per cent. from our result!

The only apparatus you see is this little grating; it is a piece of glass with four-tenths of an inch ruled with 400 fine lines. Any of you who will take the trouble to buy one may measure the wave lengths of a candle flame himself. I hope some of you will be induced to make the experiment for yourselves.

If I put salt on the flame of a spirit lamp, what do I see through this grating? I see merely a sharply defined yellow light, constituting the spectrum of vaporized sodium, while from the candle flame I see an exquisitely colored spectrum, far more beautiful than I showed you on the screen. I see, in fact, a series of spectrums on the two sides with the blue toward the candle flame and the red further out. I cannot get one definite thing to measure from in the spectrum from the candle flame as I can with the flame of a spirit lamp with the salt thrown on it, which gives, as I have said, a simple yellow light. The highest blue light I see in the candle flame is now exactly on the line. Now measure to my eye; it is forty-four feet four inches, or 532 inches. The length of this wave then is the 532d part of the four-hundredth of a centimeter, which would be the 21,280th of a centimeter, say the 21,000th of a centimeter. Then measure for the red, and you would find something like the 11,000th for the lowest of the red light.

Lastly, how do we know the frequency of vibration?

Why, by the velocity of light. How do we know that? We know it in a number of different ways, which I cannot explain now because time forbids. Take the velocity of light. It is 187,000 British statute miles per second. But it is much better to take a kilometer for the unit. That is about six-tenths of a mile. The velocity is very accurately 300,000 kilometers per second; that is, 30,000,000,000 centimeters per second. Take the wave length as the 17,000th of a centimeter, and you find the frequency of the sodium light to be 510 million million per second. There, then, you find a calculation of the frequency from a simple observation which you can all make for yourselves.

Lastly, I must tell you about the color of the blue sky which was illustrated by the spherule embedded in an elastic solid. I want to explain to you in two minutes the mode of vibrations. Take the simplest plane-polarized light. Here is a spherule which is producing it in an elastic solid. Imagine the solid to extend miles horizontally and miles down, and imagine this spherule to vibrate up and down. It is quite clear that it will make transverse vibrations similarly in all horizontal directions. The plane of polarization is defined as a plane perpendicular to the line of vibration. Thus, light produced by a molecule vibrating up and down, as this red globe in the jelly before you, is polarized in a horizontal plane because the vibrations are vertical.

Here is another mode of vibrations. Let me twist this spherule in the jelly as I am doing it, and that will produce vibrations, also spreading out equally in all horizontal directions. When I twist this globe round, it draws the jelly round with it; twist it rapidly back, and the jelly flies back. By the inertia of the jelly the vibrations spread in all directions, and the lines of vibration are horizontal all through the jelly. Everywhere, miles away, that solid is placed in vibration. You do not see it, but you must understand that they are there. If it flies back it makes vibration, and we have waves of horizontal vibrations traveling out in all directions from the exciting molecule.

I am now causing the red globe to vibrate to and fro horizontally. That will cause vibrations to be produced which will be parallel to the line of motion at all places of the plane perpendicular to the range of the exciting molecule. What makes the blue sky? These are exactly the motions that make the blue light of the sky which is due to spherules in the luminiferous ether, but little modified by the air. Think of the sun near the horizon, think of the light of the sun streaming through and giving you the azure blue and violet overhead. Think first of any one particle of the sun, and think of it moving in such a way as to give horizontal and vertical vibrations and what not of circular and elliptic vibrations.

You see the blue sky in high pressure steam blown into the air; you see it in the experiment of Tyndall's blue sky, in which a delicate condensation of vapor gives rise to exactly the azure blue of the sky.

Now the motion of the luminiferous ether relatively to the spherule gives rise to the same effect as would an opposite motion impressed upon the spherule quite independently by an independent force. So you may think of the blue color coming from the sky as being produced by to and fro vibrations of matter in the air, which vibrates much as this little globe vibrates embedded in the jelly.

The result in a general way is this: The light coming from the blue sky is polarized in a plane through the sun, but the blue light of the sky is complicated by a great number of circumstances, and one of them is this: that the air is illuminated not only by the sun, but by the earth. If we could get the earth covered by a black cloth, then we could study the polarized light of the sky with simplicity, which we cannot do now. There are, in nature, reflections from seas, and rocks, and hills, and waters in an indefinitely complicated manner.

Let observers observe the blue sky not only in winter, when the earth is covered with snow, but in summer, when it is covered with dark green foliage. This will help to unravel the complicated phenomena in question. But the azure blue of the sky is light produced by the reaction on the vibrating ether of little spherules of water, of perhaps a fifty-thousandth or a hundred-thousandth of a centimeter diameter, or perhaps little motes, or lumps, or crystals of common salt, or particles of dust, or germs of vegetable or animal species wafted about in the air. Now what is the luminiferous ether? It is matter prodigiously less dense than air, millions and millions and millions of times less dense than air. We can form some sort of idea of its limitations. We believe it is a real thing, with great rigidity in comparison with its density, and it may be made to vibrate 400 million million times per second, and yet with such rigidity as not to produce the slightest resistance to any body going through it.

Going back to the illustration of the shoemaker's wax; if a cork will in the course of a year push its way up through a plate of that wax when placed under water, and if a lead bullet will penetrate downward to the bottom, what is the law of the resistance? It clearly depends on time. The cork slowly in the course of a year works its way up through two inches of that substance; give it one or two thousand years to do it, and the resistance will be enormously less; thus the motion of a cork or bullet, at the rate of one inch in 2,000 years, may be compared with that of the earth, moving at the rate of six times ninety-three million miles a year, or nineteen miles per second, through the luminiferous ether, but when we have a thing elastic like jelly and yielding like pitch, surely we have a large and solid ground for our faith in the speculative hypothesis of an elastic luminiferous ether, which constitutes the wave theory of light.

THE LIMITATIONS OF SUBMARINE TELEGRAPHY.[8]

[8] Reproduced in abridged form from the _Electrical Review_ and the cuts from _La Lumiere Electrique.--Science_.

The weight of the conductors, says Henry Vivarez in _La Lumiere Electrique_, plays an important part in submarine telegraphy, not merely as a heavy item in the outlay, but as one of the principal factors in laying down the lines, and in taking them up in case of damage. When the conductor is being raised, the grappling-irons which lift it have to resist not merely the vertical component of the weight of the cable, but also the considerable effects resulting from friction against the water. It thus frequently happens, when working at great depths, that the conductor may be exposed to a strain greater than it is able to bear, and we are forced to have recourse to stratagems to bring it to the surface. These artifices consist in the use of two or more ships in raising, which is done as shown in Figs. 2 and 3, or, in the most simple cases, with the aid of an auxiliary buoy, as in Fig. 4. In any event, we see that the difficulties, and of course the cost of raising, must be considerable.

Hence to decrease the weight of the cables would be an important step in advance. If the weight is in general very great, it is because the copper core does not take any part in the strain which the entire cable has to resist. We know, indeed, that copper cannot bear a breaking-strain greater, at most, than 28 kilos per square millimeter. Besides, it would be elongated by such a strain by a very considerable fraction of its initial length; and, if the core were made to take part in any manner whatever in the strain which the entire cable has to support, it would be drawn out beyond its limit of elasticity, and would remain permanently elongated, while the substances in which it is inclosed would return to their natural length. It would result that, being no longer able to find room in a sheath which had become too short, the copper wire would take a sinuous form in its gutta-percha envelope, and would occasion at certain points ruptures, the effect of which would be to decentralize the wire, to perforate the layer of insulating matter, and finally to open out a fault in the cable.

But there exists an alloy (silicium bronze) which can be drawn out into wires having a conductivity equal to that of copper, and a mechanical resistance equal to that of the best iron. The use of this alloy would render it possible to set free the coating of the cables from a part of the strain which it now has to resist, and to diminish, consequently, their dimensions and weight. Wires are now made of this alloy, having a conductivity of from ninety-seven to ninety-nine per cent. of the standard, which at 0°C., and with the diameter of a millimeter, have a resistance of 20.57 ohms per kilometer. These wires do not break with a less strain than from 45 to 48 kilos. per square millimeter, and, which is a very precious property, their increase in length at the moment of rupture does not exceed one or one and a half per cent.

Let us consider the deep-sea section of cable of the French company from Paris to New York--the so-called "Pouyer-Quertier" cable, constructed and laid in 1879 by Siemens Brothers of London.

The respective weight of each of its component elements is, per nautical mile, copper core, 220 kilos; gutta-percha, 180 kilos; hemp, or an equivalent, 80 kilos; 18 wires of galvanized iron of 2 millimeters in diameter, 860 kilos; external hemp and composition, 400 kilos; total, 1,740 kilos. Total diameter, 30 millimeters. Total mechanical strength, 3,000 kilos, the wires of the covering being supposed to be of iron. Weight under water, 450 kilos. It can support its own weight without breaking for a length of from six to seven miles.

The Atlantic presents from north to south, and at about an equal distance from each continent, a sort of longitudinal ridge, in which the depths vary from 300 to 400 meters. This ridge spreads out, in 50° north latitude, into the region which has received the principal wires connecting England and France with the United States. On both coasts there are depressions in which the bottom is at the depth of from 4,000 to 6,000 meters. The one on the east extends from the south point of Ireland to the latitude of the Cape of Good Hope, and its left-hand boundary follows the general outlines of the west coasts of Europe and Africa. The two others, the northwestern and the southwestern, form two basins, bordering respectively on the United States and the Antilles and South America.

In these depressions soundings have shown certain zones in which the depths exceed 6,000 meters, the principal of which are found to the west of the Canaries, to the south of Newfoundland, between Porto Rico and the Bermudas, and to the right of the Isle of Marten-Vaz.

The great depths of the Pacific are differently distributed. Between Japan and California, between 40° and 50° north latitude, there is the Tuscarora depression, which has depths of from 6,000 to 8,000 meters. Parallel to Japan and the Kuriles there is a depression in which has been found the greatest known depth--8,513 meters.

We see, therefore, that any new great submarine line, having to extend into another zone than that which has received the present Atlantic cables, must traverse depressions in which the bottom reaches a maximum depth of 4,000 meters. The possibility of raising a damaged cable would be very problematical under such conditions, and it would become certainly impossible in case of a cable from San Francisco to Japan.

Under these conditions, we are forced to conclude that the use of the present cables limits strikingly the progress of submarine telegraphy, which must remain confined to certain zones of the Atlantic, to inland seas, and to lines along the coasts. But if we consider the daily progress of applied science, and the constantly increasing demand for rapid communication between nations, it is certain that we must shortly undertake the study of new cables intended to traverse the greatest depths of the ocean for long distances. Necessity, therefore, compels us to investigate the new solutions of the problem, which may furnish us with light cables, easy to lay, and possible to repair.

A cable made by Mr. J. Richards is composed as follows: core of silicium bronze equal in weight to that of the Pouyer-Quertier cable, or, per nautical mile, 220 kilos; gutta-percha, 180 kilos; layer of hemp, 80 kilos. The sheathing is formed of 28 wires of galvanized iron of 1.25 millimeters in diameter, each covered with hemp, and all twisted into a rope around the dielectric; the wires, 500 kilos: the hemp covering them, 250 kilos. The weight of the cable is, therefore, 1,230 kilos in the air, and 320 kilos in the water. Its diameter is 25 centimeters, and its resistance to fracture 2,800 kilos, of which the core supports one-half. Under these conditions, the cable can support from eight to nine nautical miles of its length, and can be raised from the greatest depths. The results of this comparative examination are self-evident.

For an equal conductivity and an approximately equal mechanical strength, the new cable is in weight and bulk equal to about two-thirds of the Pouyer-Quertier cable. It would cost about $165 less per mile, and would require, for laying, a ship and engines of less power, and therefore cheaper. The reduced armature will suffice to resist friction and the attacks of animal life in the deep sea; but for the shore ends we must keep to the types generally employed. Such as it is, and although it may undergo modifications in detail from a more complete study and from experience, it merits the attention of competent engineers.

WILLIAMS' SYSTEM OF COAST DEFENSE BY ELECTRICAL TORPEDOES.

Our adjoining engravings illustrate the system of J. S. Williams, for working electrical torpedoes, launches, and torpedo boats, and the appliances be proposes for their equipment and his method of utilizing a system of electrical appliances for the defense of sea-ports, harbors, coast, and coaling stations. We use Mr. Williams' own words in describing this invention. Fig. 1 illustrates men-of-war or vessels attempting to force their way into a harbor defended by such means. The movable and controllable torpedoes are indicated by letters of reference, A, connected through the medium of paying-out electrical cables, G, with the base of operations upon the shore at C, and the launches and floating torpedo batteries or vessels, D. Several lines of torpedo defense or attack are shown, and illustrate the hostile vessels coming within the destructive radius of the movable and controllable torpedoes, which radius is limited only by the length of the paying-out cable, which length can be 1½ miles (more or less). These means secure an effective weapon at all times under command from the base of operations over a radius of 1½ miles, as against a radius of 50 ft., which is the estimated effective range of destruction for fixed mines containing an equal explosive charge.

The movable torpedoes operated from the shore can be supplied with electric power from the main circuits extending along the coast from the developing source, at any distance from the electric power station or base from which the movable torpedoes are operated or supplied. Any natural force, fuel, or other means can be employed for the development of the electric force, which can be transmitted through the main circuits with high tension or pressure to the power stations along the coast, or to the floating magazines, where electric accumulators are placed to hold a reserve of energy. The accumulators at such stations can be compounded so as to be at all times ready for supplying power, and being charged, except when the limit of storage is reached. Electric cut-offs are provided in the loop or derived circuits from the main to cut the magazines out of the circuit when such predetermined limit of energy is in reserve, and means are employed to prevent the backward flow of the current toward the source from the power stations supplied from the main or other circuit. Means are also employed to automatically regulate and prevent any excess of current passing through the circuit in which the accumulators are included. The discharging circuits from the reserve magazines can be connected at the will of an operator with an electric circuit, including electric magazines, forming part of the equipment of the launches, vessels, or torpedoes, so as to supply electric power thereto. This can be accomplished at the wharves or through the medium of a cable buoyed along the coast, so as to obviate the necessity of the launches or vessels returning or running into harbor. Signaling devices can extend from such buoy to the operator along the shore, who will close the circuit from the reserve or main supply circuit. Fig. 2 illustrates a sectional elevation of an electrical torpedo provided with mechanism at the stern for operating the rudder electrically, and the force is regulated by an automatic or manually operative variable resistance interposed in the electrical circuit at the switch board of the cable. A circuit reverser and variable resistance are arranged upon the switch board, so that the operator at the base can change the direction of the current, and regulate the force applied through the medium of the electrical cable in such a manner as to adjust the rudder to port or starboard, and, if so arranged, to maintain it at any angle by varying the resistance in the circuit. The rudder mechanism can be operated by the electric energy stored on board the torpedo through the medium of an electric circuit thereto from the electric accumulator provided with a circuit closer and variable resistance worked by the force passed through the paying-out cable. The force passing there through is regulated by a pressure regulator and controlled by a circuit reverser and variable resistance upon the keyboard. Means are also employed for indicating to the operator the position of the rudder at any moment, and such position will correspond to some defined resistance introduced at any given moment in the circuit. The mechanism combined with the rudder can consist of an arrangement of compound solenoids, the armatures of which are connected to a lever on the rudder head, or a small electric motor can be employed for operating worm gearing in, or combined with, the rudder head. The rudder is brought back to the midship or normal position by springs or counterbalance weights.

The motor of the torpedo, as illustrated, is composed of a number of disk-shaped armatures fastened on the shaft, combined with the screw propeller; the field magnets, being also of disk form, are arranged so that the armatures revolve within close proximity, but not touching the pole surfaces. This enables an exceedingly high efficiency and great power to be realized from a motor of light weight. This construction of motor is specially suitable for use in the equipment of torpedoes and launches, and permits an increase of the power of the motor in either of two directions, i. e., either by increasing the number of disks of a given diameter upon the shaft, or by increasing the diameter of the disks, both of these methods giving increased power in direct ratio to the increase of size. The accumulator or secondary battery, c, is especially designed to store the energy in a small space, and with light weight, and so as to command an amount of energy representing the power necessary for a speed of 25 miles an hour or more. In the electrical circuit, between the motor and accumulator, variable resistances and other governing devices are interposed, by which the current passing to the motor is regulated automatically in accordance with the speed of the motor, or with the electric pressure in the circuit from the accumulator. A circuit closer or variable resistance operating in the circuit is connected by the cable with a variable resistance at the switch board, and operated by the current controlled thereby. The force to the motor can be regulated, controlled, or stopped at the will of the manipulator at the switch board placed at the point from which the torpedo is dispatched. Signaling devices or guide rods, O, for indicating the position and direction of movement of the torpedo to the operator can be arranged to be raised and lowered, through the medium of electrical appliances, P, at will, by a current sent through the paying-out cable from the keyboard at the base of operations. Fixed means or sight rods can be used, and hooded incandescent lamps, O_{2}, can be carried by the signal or sight rods, by which means at night or in the day the operator will be enabled to direct the torpedo to the object of attack in spite of adverse or cross currents, or a change in the position of the vessel under attack.