Thus the iron wire assumed to have a resistance of two ohms per mile has really about 5.2 ohms per mile at 160 alterations per second. Also, as seen, the true resistance is different for every rate of alternation, increasing at low rates with the square of the rate and at all time increasing rapidly with the rate. At 320 alternations the true resistance would be approximately 7.5 ohms.

Thus the apparent increase in current at the distant end by the substitution of iron wires in place of copper disappears, for the true resistance is greater and the true selfinduction less, than those values used in the calculation, and both of these factors tend to rapidly decrease the value of the receiving current.

But the mere fact of the increase in resistance with an increase in the rate of alternation would be sufficient in itself to debar the use of simple iron circuits for telephonic transmission; for as the higher overtones will be present with diminishing intensity the articulation must necessarily be poor and will grow worse as the line is increased in length. But the bi-metallic conductor which Mr. Eckert

proposes has a heavy copper deposit upon an iron core. Therefore its true resistance would be but little altered by an increase in the rate of alternation, and we should expect it to give practically as good articulation as a pure copper conductor. Also as the copper sheath forms the principal conductor for the telephonic current we should expect a volume of transmission equal to that secured by a pure copper conductor of the same conductivity, or to that secured if he should neglect to put in the iron core.

Mr. Eckert's point that a single bi-metallic conductor has an efficiency in volume and articulation equal to that secured by two all-copper metallic conductors of equal conductivity per unit length and used as a closed metallic circuit, is undoubtedly true. It is equally true with reference to a single all-copper conductor.

The addition of the "return" wire in the metallic circuit was not made either to increase the volume nor improve the quality of the transmission; both remain practically unchanged; but the earth currents which are always present to a greater or less extent, and which increase in intensity with an increase in distance, together with the inability to prevent cross-talk between parallel grounded circuits were the causes which necessitated the addition of the "return" wire.

Had Mr. Eckert reversed the position of his metals and used a conductor with a copper core and an iron sheath he would have placed his iron where it would be useful; for then he would have secured a copper conductor possessing all the advantages of an increased retardation and none of the disadvantages of a pure iron conductor, if the ratio between the iron and copper is of the proper value. The equation for the self-induction of such a circuit is

2 e

e' + 1

2

= .64. Hence, when a circuit containing distributed capacity and self-induction is brought into resonance and the current at the distant end thus rendered a maximum, there is still a considerable loss upon the line.

This is, of course, due to the short-circuiting effect of the capacity of the line and was admirably pointed out by Dr. Pupin in his lecture before the New York Electrical Society January 16, 1893.

This loss may be still farther reduced by increasing again the self-induction of the line and when the selfinduction has an infinite value the loss will be zero-so also will the current be at all points of the circuit.

This is the mistake that many writers too well known to require mentioning have made. They have aimed at secur

ing a minimum loss upon the line, which is entirely different from bringing the line into resonance and thus rendering a maximum current at the distant end.

The interesting point is that the percentage loss upon the line (36 per cent.) is independent of the length of the circuit. This however does not mean that the current at the distant end is independent of the length of circuit.

The bringing of a line into resonance increases its " resiliency "-stiffens it up, as it were. It can no longer receive the same amount of current at the transmitting end for a given impressed E. M. F, but the decreased amount which it does receive, it transmits with perfect resonance and with a uniform loss of 36 per cent.

The point has already been made in my article appearing in THE ELECTRICAL ENGINEER of January 10, 194, page 29, equation (11), that if a circuit containing distributed capacity and self induction be brought into resonance for any wave length within the range of telephonic vibrations, it will be perfectly resonant to any other. This is distinctly different from the laws of localized capacity and self induction and is the salvation of long distance telephony. For if pains be taken to bring the circuit into resonance, no matter what its length may be, the articulation will suffer no loss during transmission.

One other point in the resonance of circuits is important and instructive. The value of the current at the distant end of the circuit secured when the line is in resonance is always greater than that current which could be secured by an equal impressed E. M. F. were the line devoid of capacity and self-induction, and thus followed Ohm's law with no loss upon the line,

In conclusion then we would seem justified, in saying that were an iron sleeve .08 inch thick (or even .04 inch would yield practically identical results) added to the No. 8 B. W. G. copper wire between New York and Chicago, the circuit would be brought into resonance and the current at the receiving end would be but 36 per cent. weaker than at the transmitting end. This would bring Chicago practically 700 miles nearer New York, and would allow commercial conversation to be carried on by means of anything from the original Reis transmitter to the latest form of long distance instruments.

A more practical consideration however is, that had about one-third the amount of copper been put in the circuits between New York and Chicago, the value of a second third been placed in an iron sheath and the remaining third been allowed to repose in the pockets of the investing public, our business men of to-day who now have to surrender nine whole dollars for every five minutes conversation, would be getting more for their money and a more satisfactory article at that.

INFLUENCE OF COLD on MAGNETS AND ELECTRIC DISCHARGE IN VACUO.

Prof. Dewar is making steady progress in his wonderful discoveries as to the effects of low temperature. He gave the results of his more recent experiments in a lecture before the Royal Institution, London. The table was covered with many flasks of liquefied air enveloped in carbonic acid snow. He said he had proved that at absolute zero all metals have the same degree of conductivity to electricity, however much they may differ at higher temperatures. Prof. Gladstone's theory of refractive indices of gases had been perfectly confirmed. He found that a low temperature greatly increased the strength of metals. Iron at 180° centigrade had twice the cohesive power it possesses at an ordinary temperature.

A fully saturated magnet was found to have its power greatly increased by a reduction to 180° centigrade. Intense cold has a strange effect on color. Professor Dewar sponged a scarlet card painted with iodine with liquefied air, and the brilliant scarlet changed to orange, but recovered its original hue immediately after it became warm again. Many brilliant experiments were made by sending

electric discharges through exhausted glass globes. All the well-known phenomena of phosphorescence ceased as soon as intense cold was applied. The electricity tried to pass by any route rather than through the globe. What did this mean? asked Professor Dewar. Obviously that something was now frozen out which had before enabled electricity to pass across the vacuous space.

THE COPPER-ZINC ACCUMULATOR.-II.

BY

Daul Schoop

The explanation of what constitutes the chemical part of the Lalande cell, given in Part I, will be often referred to later on, since about the same reactions occur during the discharge of the Desmazures and of the Phillips-Entz likely the chemical or electro-chemical processes during secondary battery. Let us confess at once, that most the discharge of Lalande's battery are far from being as here set forth. The tendencies of each reaction, pointed out separately above, may be working all at the same time, each tendency contributing a certain percentage to the total amount of molecular strain which brings forth the final result.

Lalande has no doubt given a good deal of consideration to the question of electrically regenerating his discharged battery, but has never claimed to have performed it. He proposed, to "revive" or regenerate one part of the batwhereby oxygen is absorbed by the copper. It depends tery, the porous, metallic copper, by exposing it to the air, upon how finely divided or porous the spongy copper is, at caustic potash remaining in the spongy mass has been what temperature it is exposed to the air, and whether the more or less carefully washed out-whether more or less oxygen is taken up by the copper; or in other words, how far the regeneration is carried on. By washing the spongy drying the wet material to drive out all the water, and copper of the discharged Lalande cell with distilled water, finally heating it to about 300 degrees C., the regeneration is perfected and by placing this product again in the battery, the same amount of current may be again delivered from it, provided there is still zinc and caustic-potash in abundance.

Instead of regenerating the oxidized copper in this way, it can be done electrically. But it seems doubtful at first sight, whether this will be as cheap a way as the one just described. Besides, the electric method is not at all so simple. If a current is passed through the discharged Lalande cell in opposite direction to the discharge current, it will be found that the porous copper takes up oxygen and is changed into suboxide of copper, of a reddish or yellowish color, according to the nature of the reaction. But as soon as there is a trace of the higher oxidized black oxide of copper formed, the liquid near the copper side will acquire a pure blue color and, on closer investigation, will be found to contain copper.

The electrolytic liquid therefore dissolves part of the substance, formed by regenerating the copper anode. On the zinc plate, a very spongy, grey deposit will be seen, mainly at the line where the zinc plate cuts the surface of the liquid, or, if the plate be entirely submerged in the electrolyte, at its edges. This spongy substance is by no means pure zinc, but it contains a suboxide of zinc, mixed with more or less metallic zinc or, perhaps, also a compound of zinc and hydrogen. Therefore the regeneration of the zinc is not carried on by the electric current, in a regular and smooth way; it depends on the density of the current, the temperature of the cell, the composition of the electrolyte, and on a good many other points besides, how the deposit at the zinc plate is formed. Further on these points will be examined more closely; it may be mentioned here briefly,

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."

Was there a limit to the process; could the magnet already so strong continue to increase in power as more and more wire was wound in this way upon it? Henry found, after a certain length of wire had been coiled upon the iron, that the power diminished with the further increase of the number of turns. This was due "to the increased resistance which the longer wire offered to the conduction of the electricity." Had a limit indeed come to the power of the hitherto willing magnet to respond to the ever increasing demands of the young philosopher? No; Henry, undaunted, conceived a method of producing still greater power. He says:

"Two methods of improvement 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 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.""

In order to test the first method "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 helix, or variously combined into sets of lesser length." So there came into being another magnet, shown in Fig. 2. The magnetic effect was greatly increased. We quote again from Henry :

"These experiments conclusively prove that a great develop. ment of magnetism could be effected by a very small galvanic element; and also that the power of the coil was materially increased by multiplying the number of wires, without increasing the length of each.

"The multiplication of the wires increases the power in two ways; first, by conducting a greater quantity of galvanism, and secondly, by giving it a more proper direction; for since the action of a galvanic current is directly at right angles to the axis of a magnetic needle, by using several shorter wires we can wind one on each inch of the length of the bar to be magnetized, so that the magnetism of each inch will be developed by a separate wire; in this way the action of each particular coil becomes very nearly at right angles to the axis of the bar, and consequently the effect is the greatest possible. This principle is of much greater importance when large bars are used. The advantage of a greater conducting power from using several wires might, in a less degree, be obtained by substituting for them one large wire of equal sectional area, but in this case the obliquity of

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the spiral would be much greater and consequently the magnetic action less; besides this, the effect seems to depend in some degree on the number of turns, which is much increased by using a number of small wires. (Several small wires conduct more common electricity from the machine than one large wire of equal sectional area: the same is probably the case though in a less degree in galvanism)"

In Henry's cabinet were now two distinctly different magnets, one with a long continuous coil of fine wire, wound back and forth on itself; the other with a number of short thick wires; the latter much the stronger. He called the one the "Intensity" the other the "Quantity"

2. "Scientific Writings of Joseph Henry." Vol. II, p. 430.

magnet. We will let him tell why he thus designated them.

"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.

FIG. 3.-ROOM IN ALBANY ACADEMY, ORIGINALLY OCCUPIED BY HENRY.

"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."

The Institute was not insensible to the value of Henry's contribution to science and art, as the young man appeared again and again before the society, each time with magnets more powerful. These were received with enthusiasm and the fame passed beyond Albany to give their maker distinction.

Let us glance at the room that Henry occupied while making these experiments. An item recorded in one of the books of the Academy, Sept. 8, 1826, when Henry entered the Institution as a professor, tells us which room was assigned him, a room which he retained until the latter part of the year 1829: "Resolved that Prof. Henry be allowed the use of the South West Room in the third story of the Academy during the pleasure of the Board." This was Henry's work room, school room, lecture room. A long table extended across one side, and from this a series of long benches, rising in tiers one above the other filled the room. The illustration we give, Fig. 3, is from a photograph of the room as it is now, still used as a school room by the Academy.

AN ELECTRIC FREIGHT SERVICE BETWEEN ALBANY AND TROY, N. Y.

The express cars to be used by the Albany City railway company in carrying merchandise between Albany and Troy are equipped with motors and are ready to be placed in use on the road. The company have secured the building at the corner of Broadway and Nineteenth street, West Troy, for a depot, and as soon as an office shall be fitted in the building at the corner of State and Dean streets, Albany, the express line will be put in operation. It is expected the placing of the cars on the road will lead to a lively rate war with the owners of express wagons between Albany and Troy. The cars will commence running about April 1.