the plant in India) are now largely used by the paper-makers in this country, as well as in India, America and the Continent, and the wastes made in the general manufacture of jute, which cannot be spun over again, come into value in connection with paper-making, feltmaking and other purposes.

This enormous and general demand has brought about a more than equivalent producing power in this country, in India and elsewhere, and during the past few years the jute trade has been suffering from the effects of this over-production, but as the requirements of the world are increasing so rapidly, the improved demand must soon rectify this unfortunate state of things.

DIRECT MEASUREMENT OF THE INTERNAL RESISTANCE OF MAGNETO-ELECTRIC MACHINES IN MOTION.

By TH. DU MONCEL.

In a series of articles Mr. G. Cabanellas has recapitulated the means that can be employed to investigate in an easy manner the best method of working, and the current yielded by magneto-electric machines, and to allow of their being classified in the order of their merit.

One of the greatest difficulties he has encountered has been the determination of the internal resistance of the generators, with the values that result from effects produced inside the generator while in motion, and which play an important part in the formulæ deducted from the laws of Ohm and Joule. It has been known for a long time, from the researches of Le Roux, Jamin and Roger, that the resistances determined from the application of Ohm's formula to the conditions in the experiment do not correspond at all to the real resistance of the generator in repose, and that the latter should be augmented in a large proportion. (See the "Exposé des applications de l'électricité” of M. du Moncel, vol.ii, p. 271.)

It is then necessary to determine these resistances directly, so as to be able to state precisely what causes are in operation, and from them to deduct practical conclusions, and it is this which Mr. G. Cabanellas has just done in his first work which he has submitted to the Academy of Sciences. The difficulty was to avoid the induction produced by various causes which develop electro motive forces in the wire of the WHOLE NO. VOL. CX.-(THIRD SERIES, Vol. lxxx.)

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ring, rendering it impossible to measure by the Wheatstone Bridge method. The most important of these accidental inductions is that which results from the action of terrestrial magnetism, which is capable by itself alone of generating currents relatively energetic, as was shown by the experiments of M. Lami. To remove this, M. Cabanellas has opposed to one another the effects produced by it on two similar Gramme rings, moving in the same conditions, and in this manner he could determine without the intervention of that cause of disturbance the measure of the resistance of the double ring, submitted to a movement of rotation. Whether the ring was moving or in repose M. Cabanellas could make it the fourth side of a Wheatstone Bridge, and in consequence he could measure the resistance in both cases. The following are the results which he has obtained:

The resistance of the moving ring, with respect to that of the same ring maintained in a fixed position and for a mean rate of rotation of 450 turns per minute, showed an increase of about 25 per cent. (the temperature of the two rings being the same), and this increase was not at all modified by the intervention of metallic resistance introduced between the two connected rings, or outside of them. The variations produced in the electro-motive force of the generator (within the limits which allow the use of the Bridge of the Siemens Universal Galvanometer) appear to have no more influence on the measurements whether the rings were in motion or repose, and the influence of weights applied to the collectors of the rings produced differences only of a secondary order. With powerful electro-motive forces, it has been the same, but M. Cabanellas has employed for verification an arrangement of two galvanometers, one of low resistance placed in the circuit, and one of great resistance placed in a shunt, which has enabled him to obtain direct measurements, without necessitating the use of standard resistances specially made of large wire. E The resistance of each ring was then given by the proportion

QI

It would have been interesting to study the manner by which the increase of resistance varies with the speed of rotation of the rings, so as to fix the laws of the phenomena, but the experiments made at the establishment of Messrs. Sautter, Lemonnier & Co. required such great derangements of the business that M. Cabanellas, not willing to abuse good nature, has postponed the further experiments which he intends to make.-La Lumière Electrique.

THE THEORY OF THE TELEPHONE.

Our readers will remember that in 1879 M. Ader constructed a telephone without a diaphram, the sound being given out by a soft iron wire enclosed in a helix, through which the current passed. The action was explained by du Moncel as due to longitudinal vibrations in the wire resulting from successive lengthenings and shortenings of the wire under the action of the magnetizing helix, it being well known that an iron core is lengthened by magnetization. M. du Moncel employed this fact to support his molecular theory of the action of the Bell telephone. Since that time M. Boudet, of Paris, has, by means of his sensitive microphone, succeeded in revealing these changes of length. Moreover, M. Ader himself has investigated the subject very closely, and besides measuring the effect in question has arrived at the important principle that all bars of magnetic nature submitted to a mechanical action, be it compression, torsion or tension, tend to recover their primitive molecular arrangement under the influence of the current which magnetizes them.

The apparatus employed by M. Ader in his experiments consists of a small straight electro-magnet, having its core formed of an iron wire 0.04 or 0.05 metres long, and one extremity chamfered off. Upon this chamfer acts a long lever, which serves the double purpose of an indicator and exciter of the mechanical action. The lever terminates in an index which moves itself before a graduated scale (in front of which is a lens) and is connected to the magnetic core in a manner differing with the mechanical action to which the latter is submitted.

In the cases where compression and tension are produced two distinct effects are seen. On allowing the current to flow for several instants continuously the index is gently displaced, moving up the scale in the former case (compression) and down the scale in the latter case (tension), with a deflection proportional to the intensity of the battery and the time of the closure of the current. This effect is evidently due to the dilation of the core in each case under the influence of the heat developed by the current, for it is obtained with a core of copper. On closing the circuit momentarily the lever rises instantly in both cases, and instantly falls on the current being interrupted. At the same time a "dry" sound can be perceived at each make and break of the cur

rent when the ear is applied against the table supporting the apparatus. But the apparatus is so arranged that the displacements indicated in the two cases correspond to two mechanical effects diametrically opposite in character-that is to say, to a lengthening and shortening of the core. It can, therefore, only be due to a molecular action tending to annul the mechanical strain on the core in either case.

In the case of torsion, the index rises always at the moment of making the circuit and falls again at the moment of breaking it, and in a degree corresponding to the force of the mechanical action, as can be determined by a weight sliding on the torsion lever. In this case the thermal effect is not shown at all, since the indicating lever does not change its position by reason of the lengthening or shortening of the magnetic needle. The magnetization in this case tends, as in the experiments of MM. Guillemin and Coulon, to untwist the wire.

The length by which the core is shortened by closing the circuit momentarily by the current, according to M. Ader's calculation, is less than one ten-millionth of a metre, or one ten-thousandth of a milliIt is greater under the influence of torsion, and less under the influence of tension.—The Electrician.

metre.

Mechanical Theory of Heat.-In Jacob Hermann's Phoronomia sive de Viribus et Motibus Corporum solidorum et fluidorum, libri duo, 1716, sections 658 and 659 treat of the internal movement of fluids and of heat as dependent upon molecular motion. The latter section contains a demonstration of the theorem that "heat, other things being equal, is in a ratio compounded of the density of the heated body and of the duplicate ratio of the disturbance of each one of its particles. Ann. d. Phys. u. Chem.

C.

Occlusion of Gases in Aluminium and Magnesium.—M. Dumas finds that not only iron and silver possess the property of retaining large amouuts of gas for an indefinite period, but that aluminium and magnesium also have the same property. For equal weights magnesium contains a volume twice as great as aluminium. But magnesium is so much lighter than aluminium that it will hold only one and a half times its own volume. Silver seems to prefer oxygen; aluminium and magnesium hydrogen, each metal appearing to have its individual preference.-Comptes Rendus.

C.

New Magnetical Experiments.-M. Ader has performed some interesting experiments upon bodies which are slightly magnetic. He finds that elder pith is more sensitive than ordinary wood, paper, etc. With a Jamin magnet, sustaining a weight of 100 k. (220-46 lbs.), and provided with two small polar armatures, separated by an interval of 2 mm. (78 in.), he has been able to attract, at a distance of 3 mm. (*118 in.), a pith ball of 5 mm. (02 in.), suspended by a thread. He has been able even to raise it, and when once attached to the magnet considerable force is necessary in order to remove it.-Comptes Rendus.

C.

Discovery of a New Elementary Body in the Lava of Vesuvius.-Prof. Scacchi, the celebrated mineralogist and crystallographer, in studying the yellow incrustation which is found on certain portions of the Vesuvian lava ejected in 1631, and which he calls Vesbine, has discovered a body which differs in its character from all the known elements. He considers Vesbine as a vesbiate of alumina, and he regards vesbic acid as the oxacid of a new element, vesbium, which, according to the properties of its compounds, will probably stand between molybdenum and vanadium. Stas thinks that vesbium may be found in some of the common ores, where its presence has never been suspected because it has been confounded with some of the known acidifiable metals. Bull. de l'Acad. Belg. C.

Influence of Light, Copse and Mould on Forest Growth. -M. Gurnaud has conducted a series of observations, during the past nineteen years, upon the solid contents of annual growth in a forest among the Jura mountains. He finds that: 1. Light, when it strikes the ground without having been sifted by foliage, stimulates the production of carbonic acid in the decompositions which are engendered by the humus, together with a decomposition of the same gas by the chlorophyll. 2. The growth of wood diminishes when the underbrush intercepts, to any great extent, the access of light to the soil and diminishes its reflex action on the branches of the trees. 3. This interruption of reflex action is due mainly to the spread of the underbrush, for when it is kept trimmed the vertical shoots which are retained interpose no obstacle. 4. The mould, under too great a thickness, loses a part of its virtue, and, like barn-yard manure which is too deeply buried, remains inert for many years.-Comptes Rendus. C.