come the resistance offered by the rarefied medium through which it must flow.

EARTH-CURRENTS ON TELEGRAPHIC LINES.

The Asiatic Society of Bengal, in consideration of the important labors of Mr. Schwendler, has taken steps to influence the government of India to especially investigate the subject of earth-currents on telegraph lines-a work which ought, in the interest both of science and art, to be taken up not only by the European governmental, but by American private telegraph companies.

ON UNILATERAL CONDUCTIVITY OF ELECTRICITY,

While engaged in other work, Dr. Schuster states that he met with an irregularity which seemed to be of such a peculiar nature that he subjected it to a separate investigation; although he is not yet able to raise this phenomenon above the rank of an irregularity, yet his experiments leave no doubt as to the fact. It seems to him clear that the current produced by an electro-motive force in a circuit composed entirely of copper wires, joined together by means of binding screens, may under certain circumstances be different from the current produced by the same electro-motive force acting in an opposite direction. He calls this phenomenon. "Unilateral Conductivity." The most plausible explanation seems to him to be that a thin layer of air may sometimes intervene between the two wires that are screwed together, an explanation that has been confirmed by some experiments, while others show that it is insufficient.-7 4, XLVIII., 246.

THE ELECTRIC CHARGE OF A CONDUCTING WIRE.

The researches of various physicists have proved that an electric current, before it can circulate in any conductor, must charge it electrically, and consequently in the entrance of a current into the circuit two periods are distinguished. In the first the wire is charged, the current passing through a variable state until it gradually acquires its normal value. In the second period the current has become constant, and its value depends on the conditions determined by Ohm's law. According to Villari, the first or variable state has no constant duration; it increases with the length and condition

of the circuit, and also with the so-called co-efficient of charge of the wire, which co-efficient is measured by the quantity of electricity necessary to give a unit's charge to a unit's length of wire. This co-efficient of charge varies with every metal, and with it varies the duration of the current's variable state; the quantity of electricity which the current consumes to establish itself is with the different metals also variable.-18 A, XX., 4.

THE ACTION OF ELECTRICITY ON PHOSPHORUS.

In 1860 Dr. Giessler endeavored to show that electricity of itself can effect the conversion of ordinary phosphorus into amorphous phosphorus. An apparatus recently devised by Schwendler shows that the conversion of the phosphorus is effected even by the inducing action of the current of electricity. For this purpose the ends of two conducting wires are inserted into exhausted spheres in which there is no phosphorus. These spheres are inclosed in others, and the space between (likewise exhausted of air) contains the phosphorus, which is therefore completely shut off from the conducting wires by a screen of glass. On the passage of a current the sides of the spheres become coated with amorphous phosphorus. It may be considered demonstrated that this conversion is effected neither by the light nor by the heat that accompany the current, but exclusively by the electricity itself.

THE DIFFERENCES BETWEEN VOLTAIC AND FRICTIONAL

ELECTRICITIES.

In reference to the difference between electricity developed by friction and that developed in the galvanic battery, it has long been remarked that the former, or electricity of high tension, as it is called, excels the other in the development of light by the electric spark, and has a stronger phys iological effect upon the nerves and muscles, while its chemical, thermic, and electro-magnetic effects are much weaker. A further difference between these two sources of electricity consists in this, that the galvanic current follows the law of Ohm, varying its intensity with the resistance between its poles, while the current from the electric machine, as was shown by Gauss, remains constant, no matter how great the

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resistance of the bodies penetrated by it. The study of the failure of Ohm's formula in this case has been the subject of an investigation by Rossetti, who, among many other conclusions, establishes the following principles: In one and the same series of experiments, conducted under identical circumstances with reference to atmospheric humidity, the intensity of the current excited by the electric machine is nearly, but not exactly, proportional to the velocity of the revolving disk. The relation between the velocity of the disk and the intensity of the current is not independent of the moisture in the air, but varies sensibly therewith, the number of turns the disk must make in a second, in order that a current of constant intensity may be developed, is greater on moist than on dry days. The work required to make the electric machine active is exactly proportional to the intensity of the current, assuming that the humidity remains the same. The ratio between the work and the intensity of the current diminishes with increasing moisture, so that in order, on a moist day, to obtain a current of given intensity, there may indeed be required a greater velocity of rotation; but equally is it true that a less amount of work would be expended, so that the electric machine is more economical on moist days than on dry.-19 C, VIII., 140.

NEW MODIFICATION OF THE LECLANCHÉ BATTERY. M. Kern, of St. Petersburg, after detailing several grave objectionable qualities of the Leclanché cell, at present very popular for telegraphic and other uses, recommends the following modification, which he claims will act very constantly. Two parts of well-washed coke and one of manganese dioxide, in the state of powder, are well mixed together with a small quantity of water acidulated with some drops of nitric acid, and the mixture is then pressed into a cylindrical mould of suitable size. The resulting coke-manganese cylinders are dried in a warm place, but not over a fire, as a strong heat will decompose the peroxide. The dried cylinders are placed in glass jars containing concentrated solution of ammonium chloride, and surrounded with zinc plates curved in the usual manner. By this arrangement the use of porous cells is avoided, and a battery of such elements acts more constantly, besides which the construction is materially cheap

ened. For the glass jar, the author furthermore substitutes a wooden box of the same size, coated with a mixture of wax, two parts; resin, ten parts; red-lead, two parts; and gypsum, one-sixth part.-1 A, XXXI., 203.

SIMPLE METHOD OF MAKING CARBON CELLS.

Mr. Symons gives the following method, as practiced by himself, for constructing plates or cells of carbon of any required shape and size, such as are used in galvanic batteries. With a sirup of equal quantities of lump sugar and water, mix wood charcoal, in powder, with about equal parts of the light powder called vegetable black. The mixture should hang well to the moulds dipped into it, and yet be suffi ciently free to form itself into a smooth surface. Moulds of the cells required are made of stiff paper, and secured by wax or shellac. These moulds are dipped into the carbon sirup, so as to cover the outside only, and then allowed to dry. This dipping and drying ought to be repeated until the cells are sufficiently thick; when well dried they are buried in sand, and baked in an oven hot enough to destroy the paper mould. After being cleared from the sand and burned paper, the cells are soaked for some hours in diluted hydrochloric acid, and again well dried, then soaked in sugar sirup. When dried, they are packed with sand in an iron box, gradually raised to a white heat, and left to cool. If some of the cells be cracked, they need not be rejected, but covered with paper or plaster and dipped into melted paraffin. Rods or plates of carbon can be made by a similar process. The carbon thus made will be found to have a good metallic ring, and a brilliant fracture.-12 A, XI., 8.

NEW ABSOLUTE GALVANOMETER.

An absolute galvanometer is described by Professor Guthrie, as constructed for him by the Messrs. Elliott. Its principle consists in the determination of the strength of the cur rent, by the measurement of the mechanical force necessary to bring to within a given distance of one another two electro-magnets which are affected by the current in such a manner that they repel one another. The galvanic current whose force is to be measured coils around two fixed soft iron masses, rendering them magnetic, and then around

two movable soft iron masses suspended by a vertical thread. Many of the laws of electro-dynamics may be readily illustrated by this instrument, and not only may different currents be compared with the greatest accuracy, but the absolute mechanical value of the current may be at once arrived at.-7 A, XLVIII., 297.

EARTH CURRENTS IN TELEGRAPH LINES.

Mr. Schwendler, who in 1868 was intrusted with the introduction of a system of testing telegraph lines in India, took that opportunity to do his work so thoroughly as to secure all the data necessary for the quantitative determination of the electro-motive force on the line. Over 10,000 determinations have been made during the past six years, and he deduces from these the conclusion that all the lines in India are affected by natural currents of electricity. These currents are, as it were, a negative or copper current, flowing from the east to the west. The strength of the natural current is very variable, even on the same line. The direction is also variable, but far more constant than the strength. The variations in strength and direction, on parallel lines of telegraph, are very uniform. The prevailing direction of the current is generally also the direction of the maximum current. He considers himself now fully justified in establishing further improvements for the purpose of minutely investigating these currents, and his propositions having been strongly urged upon the attention of the Indian government, have been favorably received by it.-Proc. Asiatic Soc. Bengal, June, 1874, 145.

VARIATIONS OF SHIPS' COMPASSES.

Sir William Thomson communicates to the British Association for the Advancement of Science an investigation of the perturbations of the compass produced by the rolling of the ship-the so-called "heeling error" which has been studied by Airy and Smith. This heeling error may be defined as the angle between the directions for the ship upright and the ship inclined, the resultant of the horizontal magnetic forces of the earth and the ship at the position of the compass-a definition that would be rigorous for a compass supported on a point in the ordinary manner, if this bear