that as soon as a trace of the blue copper containing liquid reaches the zinc plate, a black deposit of finely divided copper is immediately observed on the zinc. At this stage local action is set up between the trace of copper and the zinc plate, causing the zinc to oxidize and dissolve in the alkaline liquid, while gaseous hydrogen escapes freely from the deposited copper. 1

The Desmazures Battery. With a view to facilitating the electrical regeneration of the Lalande battery, Mr. Desmazures has given it an entirely different construction and has been forced to alter every single part of it correspondingly. The anode or the copper part is made by compressing finely divided copper-as obtained for instance by mixing precipitated oxide of copper with zinc powder and pouring this mixture into a solution of caustic soda, or as obtained by certain galvanic reactions--on a network of copper-wire. The pressure is about 1,000 atmospheres.

In this way, a plate of porous copper is obtained, about 3 mm. thick, and of sufficient mechanical strength to stand all the handling and shocks of practical use. The specific gravity of this copper plate, although it is pretty firm and hard, does not exceed 4.1 (about one-half of the specific gravity of the solid copper) and absorbs with great facility the bodies deposited by the galvanic reactions on its surface. The plate is surrounded by a frame and provided with a proper connection and then put in an envelope of parchment paper. A grid of insulating material, such as whiting or similar substance, insoluble in the alkaline liquid, is put on both sides of the plate and again an envelope of parchment paper is applied around the whole structure. In this way, the total thickness of the anode is about 7 millimetres.

The cathode, or that electrode at which the zinc is deposited, consists of three pieces of steel wire network, held together by an outer frame of sheet steel and a connection piece on top of the plate, which is rivetted to the steel network. Plugs of insulating material are attached to the plate, in order to keep it at uniform distance from the anode. Instead of insulating plugs, a grid of ebonite may be laid on each side of the cathode, so that the thickness of this part amounts to about 8 or 9 millimetres.

The box is made of sheet steel of 1 mm. thickness. The copper plate and the steel wire plates are placed alternately in the box, and the plates pressed tightly together. The connections are made by screwing all the copper connectors together and the same is done with all the steel connectors. The box is provided with an air-tight cover of sheet steel, through which the two poles of the cell enter. A little valve for the outlet of gases is also fixed on the cover.

The electrolyte consists of a concentrated solution of caustic-potash with a certain percentage of zinc dissolved in it and containing also some mercury. Its specific gravity is about 1.6; the liquid is colorless and without any odor. It is covered with paraffine oil, to prevent the absorption of carbonic acid from the air. The addition of mercury to the liquid greatly facilitates the proper deposition of zinc and suppresses also part of the local action between the deposited zinc and the liquid.

It is claimed by the inventor of this battery that its efficiency is even superior to that of any type of the lead accumulator. No current is lost during the charging of the battery, since no gas is developed even by overcharging. The internal resistance of the cell is given as 0.35 ohm per square-decimetre surface of plates (average). The efficiency in watt hours is given as 80 per cent. under normal conditions. The reliability, durability and convenience in handling this battery are stated to be superior to that of a lead cell, while the output of electric energy per unit of weight is claimed to be at least 14 times as great as that of the best and lightest lead cell.

1. Professor H. S. Carhart, in his book, "Primary Batteries," gives a splendid description with illustrations of three different types of the Lalande battery, and most careful and scientific tests of the Edison-Lalande type. The perusal of Professor Carhart's book is highly recommended to all interested in this subject.

It is important to keep this copper-zinc accumulator free from contamination with ammonia, nitric acid, chlorine, or any like substances, liable to attack the copper or steel in the cell.

THE ELECTRO-MAGNET; or JOSEPH HENRY'S PLACE IN THE HISTORY OF THE ELECTRO-MAGNETIC

TELEGRAPH.-IV.

BY

Mary A. Henry

Still brooding over the theory of Ampere, Henry was not content. The current was still led, although in a less degree, in an oblique direction, and not at right angles to the length of the iron bar. Sitting one evening at home in his study, lost in a deep revery, although a friend was with him, the idea came to him that he could obtain the condition the theory required by winding the wire backward and forward in several layers around the iron core.

"The successive spirals of wire, coiling first in one direction then in the other, would tend to produce a resultant action of the current at right angles to the core, and that furthermore in the great number of revolutions thus obtained the current would act on a greater number of molecules of the bar and so excite greater magnetism."

He sprang to his feet, and striking his hand upon the table near him exclaimed: "To-morrow I will make an experiment which in its result will astonish the world." "When the conception," he said, " came into my brain, I was so pleased with it I could not help rising to my feet and giving it my hearty approbation!" (If this seems at variance with Henry's well-known and great modesty it must be remembered that it was an involuntary expression of delight, uttered only in the presence of a very intimate friend. Even modesty could not blind his eyes to the value of his researches in their bearing on the telegraph, which at this time, as later, he fully recognized). He made the experiment the next day, and to his delight and encouragement success again rewarded him.

He tested his theory on the magnet we have just described as lifting fourteen pounds. Over the wire, which was already closely wound on the iron core, he wound another insulated wire, in such a way as to give the effect of a long continuous wire wound upon itself. He says:

"A second wire of the same length as the first was wound over

it, and the ends soldered to the zinc and copper in such a manner

that the galvanic current might circulate in the same direction, or, in other words, that the two wires might act as one; the effect by this addition was doubled, as the horse-shoe, with the same plates before used, now supported 28 lbs. With a pair of plates, 4 inches by 6 inches, it lifted 39 lbs., or more than fifty times its own weight."

Where was Sturgeon's magnet now, lifting only its nine pounds with its battery of one hundred and thirty plates, in comparison with this magnet of Henry's sustaining fifty times its own weight under the influence of only a single pair of plates? Fig. 1.

"The same principle," Henry says "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."

"In the arrangements 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 upon and 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."

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 development 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.

"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.

in one of the windmills at the works of Mr. A. J. Corcoran, Jersey City, N. J., the well-known builder of windmills, and during a recent visit of the writer to these works the operation of the system was demonstrated to its fullest advantage. The simplicity of the plan is well shown in the accompanying engraving which illustrates such a plant in all its details. The dynamo driven by belt from the main gear, charges a set of storage batteries. It is so designed that throughout the wide variations of speed of the windmill it maintains the potential constant. The automatic switch, which constitutes the only auxiliary apparatus in the entire system, is so arranged as to close the circuit to the battery when the dynamo speed is such as to generate an E. M. F. equal to the counter E. M. F. of the battery. At this point the cells begin to be charged and as soon as the dynamo pressure falls below the required potential, the cut-out acts so as to prevent the battery from discharging through the dynamo. The switch is so designed that it opens and closes the circuit when the current itself is at zero, and hence no sparking occurs at the contact points, while the brushes on the dynamo remain fixed under all conditions of working.

The Corcoran mill at Jersey City has a diameter of 18 feet and at a speed of 20 miles an hour is capable of delivering 3 h. p. The dynamo is driven by belt in the manner shown, having a maximum current capacity of 35 amperes at 35 volts and is cut into action when the speed is 600 rev. per minute, that is, when an 8-mile breeze is blowing. The machine is of the iron-clad type, entirely enclosed and occupies a floor space of only 30 inches square and 15 inches high.

The plant, though merely an experimental one, has operated without a single mishap from the start and the storage cells furnish current for 24 incandescent lamps distributed through the work shops.

The smoothness of working and the evident reliability of the entire arrangement leave little room for doubt that we shall see a wide application of this system.

THE TESLA CONDENSER-MAGNET.

In electric apparatus or systems in which alternating currents are employed, the self-induction of the coils or con

ductors in many cases operates disadvantageously by giving

rise to false currents which often reduce the commercial efficiency of the apparatus or operate detrimentally in other respects.

The effects of such self-induction, as is well known, can be neutralized by proportioning to a proper degree the capacity of the circuit with relation to the self-induction and frequency of the currents. This has been accomplished heretofore by the use of condensers applied as separate instruments. In order to avoid the employment of condensers, which involve additional expense, Mr. Nikola Tesla has devised a method of constructing the coils themselves so as to accomplish the same object as the condensers.

Mr. Tesla had found some years ago that in every coil there exists a certain relation between its self-induction and capacity that permits a current of given frequency and potential to pass through it with no other opposition than that of ohmic resistance, or, in other words, as though it possessed no self-induction. This is due to the mutual relations existing between the special character of the current and the self-induction and capacity of the coil, the latter quantity being just capable of neutralizing the selfinduction for that frequency.

It is well known that the higher the frequency or potential difference of the current, the smaller the capacity required to counteract the self-induction; hence, in any coil, however small the capacity, it may be sufficient for the purpose stated if the proper conditions in other respects be secured. In the ordinary coils the difference of potential between adjacent turns or spires is very small, so that

while they are in a sense condensers, they possess but very small capacity and the relations between the two quantities, self-induction and capacity, are not such as under any ordinary conditions satisfy the requirements contemplated by Mr. Tesla, because the capacity relatively to the self-induction is very small.

In order to attain his object and to properly increase the capacity of any given coil, Mr. Tesla winds it in such a way as to secure a greater difference of potential between its adjacent turns, and since the energy stored in the coil -considering the latter as a condenser-is proportional to the square of the potential difference between its adjacent convolutions, it is evident that in this way he may secure, by a proper disposition of these convolutions, a greatly increased capacity for a given increase in potential difference between the turns. The accompanying drawings show the general nature of the plan which he has adopted for carrying out this idea.

Fig. 1 is a diagram of a coil wound in the ordinary manner, while Fig. 2 shows the winding designed to secure the objects Mr. Tesla is aiming at.

In Fig. 1, A designates any coil the convolutions of which are wound insulated in the usual way. Let it be assumed that the terminals of this coil show a potential difference of 100 volts, and that there are 1,000 convolutions; then considering any two contiguous points on

adjacent convolutions let it be assumed that there will exist between them a potential difference of one-tenth of a volt.

parallel with the conductor A and insulated from it, and If now, as shown in Fig. 2, a conductor в be wound the end of a be connected with the starting point of B, the aggregate length of the two conductors being such that the assumed number of convolutions or turns is the same, viz., 1,000, then the potential difference between any two adjacent points in A and B will be 50 volts, and as the capacity effect is proportional to the square of this difference, the energy stored in the coil as a whole will now be 250,000 times as great.

Based on this principle, any given coil may be wound either in whole or in part, not only in the exact manner illustrated, but in a great variety of ways, so as to secure between adjacent convolutions such potential difference as will give the proper capacity to neutralize the self-induction for any given current that may be employed. Capacity secured in this particular way possesses an additional advantage in that it is evenly distributed, a consideration of the greatest importance in many cases, and the results both as to efficiency and economy are readily and easily obtained as the size of the coils, the potential difference, or frequency of the currents are increased.

THE TROLLEY AND INSURANCE.

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THE New York Board of Fire Underwriters' special committee on electrical hazards called upon Mayor Gilroy recently and protested against the introduction of the trolley upon Manhattan Island, also warning the Mayor that if the trolley was introduced the inevitable result would be an increase in fire insurance rates.