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.-7 A, 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.-Poggendorff Annalen, CLII., 486.

MEASUREMENTS OF TERRESTRIAL MAGNETISM.

Attention is called by Braun to the practicability of ap plying 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 incli

nation 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.-Iaanel's Inaugural Dissertation, Breslau, 1873, 128.

THE EFFECT OF MAGNETISM 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

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 upon 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.- Poggendorff Annalen, CLII., 494.

THE 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

ous gases, sealed up in Geissler tubes, have been experimented upon, the discharge from a Ruhmkorff coil being allowed to traverse the gas. Changes occur in the appearance of the luminous discharge where the magnet is excited; these changes are accompanied by a change in the resistance of fered to the current by the gas. Thus a tube containing hydrogen permitted the passage of a current marking twentyfive degrees on the galvanometer when the magnet was not excited, but when excited the galvanometer reading was forty degrees. It seems to be a law that the augmentation in the intensity of the current is greater with a gas which is a good conductor than with one which is a bad conductor.-12 A, XL., 19.

NEW SOURCE OF MAGNETISM.

M. Donati Tommasi is authority for the statement that if a current of steam at a pressure of from five to six atmospheres is passed through a copper tube of two to three millimeters in diameter, which is spirally coiled about an iron cylinder, the latter is magnetized so effectually that an iron needle, placed at the distance of some centimeters from the steam magnet, is strongly attracted, and remains magnetic. so long as the steam is allowed to pass through the copper spiral.-6 B, XV., 1875.

MAGNETIC PERMEABILITY OF IRON, NICKEL, ETC.

Mr. Rowland, of Troy, New York, in a paper on the magnetic permeability of nickel and cobalt, states that the views of the English and German philosophers as to the nature of force have given rise to different ways of looking upon magnetic induction. Thus, the Germans would say that this action was due in part to two causes-the attraction of the coil and the magnetism induced in the iron by the coil; the English, following Faraday, on the other hand, would consider the substance in the helix as merely conducting the lines of force, so that no action would be exerted directly on the compass needle by the coil; but the latter would only affect it in virtue of the lines of force passing along its interior, and so there could be no attraction in a perfectly vacant space. According to the first theory, the magnetization of the iron is represented by the excess of the action of the

electric magnet over that of the coil; while by the second theory, when the coil is very close around the iron, the whole action is due to the magnetism of the iron. The natural unit of magnetism to be used in the first theory is that quantity which will repel an equal quantity at a unit's distance with a unit of force. On the second theory, it is the number of lines of force which pass through a unit of surface when that surface is placed in a unit field perpendicular to the lines of force. As the result of his novel and very important researches on the effect of heat on magnetism, Rowland states that if it were possible for the magnetism of substance to attain a maximum value, the co-efficient of magnetism by induction would become, first, zero, and then negative, and the substance would then become diamagnetic for very high magnetizing forces. This principle, announced independently by Maxwell and Rowland, lacks as yet the confirmation of observation, although not contrary to our experience. Our principal hope of confirming it by observation consists in heating some body, and then subjecting it to a very high magnetizing force, for Rowland has shown in the case of iron and nickel the maximum of magnetization of nickel and of iron decreases as the temperature rises, at least between the limits of zero and 220° Centigrade. He finds from observation that if nickel is heated from 15° to 220° Centigrade, the magnetization will increase if the magnetizing force is small, but will decrease if it is large. In general, as the magnetizing force is increased, the resistance of iron, nickel, and cobalt to magnetization decreases, until a minimum is reached when the metals have attained a magnetization equal to from 24 to 30 per cent. of their maximum of magnetization, and after that resistance increased indefinitely.-7 A, XLVIII., 32.

IMPROVEMENTS IN THE GRAMME MAGNETO-ELECTRIC MACHINE.

The magneto-electric machine invented by Gramme, which has within the past two years become quite famous, has received an important improvement in that ordinary magnets have been replaced by the plate magnets invented by Jamin, which give it a great advantage, not only because of the greater force for the same weight, but because of the extreme facility of their construction. These plate magnets can be built up and taken apart in a few minutes, an ex