« ÎnapoiContinuați »
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 sufficiently 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 current, 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, bave 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
ing point were carried by the ship uniformly in a straight line, and is sufficiently approximate when the compass is placed in the ship's axis of rolling. The perturbation produced in the compass by this rolling will be solely that due to the variation of the horizontal component of the ship's magnetic force. Such a position of the compass would have one great advantage, viz., that the application of proper magnetic correctors adjusted by trial, to do away with the rolling error, would also perfectly correct the heeling error.–74, XLVIII., 364,
THE FORMATION OF MAGNETS BY ELECTROLYSIS. In a recent notice of the labors of Jacobi, Beetz considers the question of the formation of magnets by electrolysis. The latter states that on causing iron to be deposited by galvanic action in the interior of a coil, he subsequently found the iron to be magnetic. To secure this result his cathode was a plain metallic plate, opposed to a similar iron plate which acted as a node. An attempt by Jacobi to produce similar action seems to have failed, and the reason for its failure is explained by Beetz as resulting principally from the fact that the electrodes employed by Jacobi were of such a nature, and so arranged, that it was impossible to induce any magnetism in the iron deposited between them; in fact, the molecules of the latter were deposited in a magnetic shade so intense that less than 0.01 of the electro-motive force affected it.—Poggendorf' Annalen, CLII., 486.
MEASUREMENTS OF TERRESTRIAL MAGNETISU. Attention is called by Braun to the practicability of applying the inclinatorium to the determination of the intensity of terrestrial magnetism. This was first suggested and applied by Lamont and Lloyd, but seems to have been generally neglected. Braun, however, shows that both theory and practice agree in proving that this method allows of the same degree of accuracy as that attainable by the best magnetometers. In detail he finds that Lloyd's method gives the total intensity more accurately than the horizontal intensity, but by the magnetometer method the reverse is the case. The accuracy of the results obtained by Braun is attributed, in part, to the great perfection of the inclination needles that are now made in England, and he recommends earnestly the inclinatorium as a portable magnetic instrument, upon the score of accuracy, convenience, and cheapness; since with it one may make a complete series of magnetic observations, without also carrying declinometer, magnetometer, reflecting circle, theodolite, or clock. A simple addition to the instrument even allows him to make absolute as well as relative determinations. - Poggendorff Annalen, CLII., 619.
NEW METHOD OF INVESTIGATING TERRESTRIAL MAGNETISM.
In an inaugural dissertation of Dr. Haanel, of Albion, Michigan, recently printed at Breslau, Germany, the advantages of the galvano-metric method for the determination of the earth's magnetism and its oscillations are elucidated; he concludes that the method is well adapted to such determinations, and that it will recommend itself by the following advantages: The instrumental constants need be determined only once for all subsequent observations; the oscillations of the declination may be eliminated by properly arranging the observations; Gauss's method of counting the vibrations is dispensed with; the magnetic power of the coil can be increased or diminished at pleasure; and the oscillations of the coil are under perfect control of the observer.-llaanel's Inaugural Dissertation, Breslau, 1873, 128.
THE EFFECT OF MAGNETISH ON THE ELECTRIC DISCHARGE.
The last work published by A. De la Rive relates to this subject, in the early development of which he took so active a part, namely, the effect of magnetism on the electric discharge when the latter takes place through a rarefied gas. In an earlier memoir on this subject he studied the case of the magnet acting upon a discharge, the latter being perpendicular to the magnet. He showed that in this case the magnetism produced not only a deviation of the luminous jet, but its condensation, its more intense brilliancy, and a notable diminution of the elastic force of the gas in the portion of the discharge which is more directly submitted to the magnetic action. This augmentation of intensity varies with the nature of the gas. It is least with hydrogen and greatest with air; that is to say, the effect is more marked
2012 gen POTT
501 Dest bol nita!
in proportion as the gas is a less good conductor of electricity, and the effect is more considerable on that portion of the discharge near the electrode than upon the rest of the column. The electric conductivity of the gas also diminishes, owing to the action of the magnet, and by a quantity that varies very notably with the nature of the gas, being so much more considerable as the gas is a better conductor of electricity. As the result of his later investigations, De la Rive finds that when the magnet is presented to the gas influenced by the electric discharge in such a way that the axis of the magnet is not perpendicular, but parallel to the axis of the discharge, and is, in fact, a continuation of the latter, then all the preceding phenomena are reversed. Further experiments showed that a special and peculiarly intense resistance, having its seat at the issue from the negative electrode, is that which is overcome by the intervention of the magnet. The dimensions of the negative electrode notably influence the dimensions of the aureola.—7 A, XLVII., 464.
FORMATION OF MAGNETISM BY ELECTRIC CURRENTS. Some researches made by Beetz into the possibility of communicating permanent magnetism to the iron deposited by galvanic currents have an interesting bearing, not only upon chemical, but also npon geological theories; he states as the result of investigations into the influence of the chemical nature of the solution employed as an electrolyte, that the iron deposited from solutions containing sal ammoniac is in a peculiar manner susceptible to the reception of permanent magnetism. If the deposition takes place under the influence of a strong magnetism, avoiding injurious circumstances, there are formed from the sal-ammoniac solution strong magnets of uniform structure, while from solutions having no sal ammoniac magnets are formed whose structure is irregular, and whose magnetic power is quite feeble.- Pog. gendorff Annalen, CLII., 494,
TIE INFLUENCE OF A MAGNET UPON THE GALVANIC ARCH.
Messrs. Delarie and Sarasin have published the result of some experiments concerning the effects of magnetism on the electric discharge through rarefied gas when the discharge occurs in the prolongation of the axis of the magnet; vari