Short Bar Research Articles

NEW SPECIES OF NORTH AMERICAN LEPIDOPTERA

Fore wings white, with small orange patch at apex, marked with black dots and bars as follows: Six spots on costa, about equidistant, the basal one slightly removed from costa and the second smaller than the others, a round spot in cell, followed by four short parallel transverse bars beyond it, lying close together, the third one joining spot on costa. A short longitudinal dash on inner margin at base, followed by five transverse bars from median vein to inner margin, the first, however, not quite reaching it. Of these the third and fifth are narrower than the others and in the male especially tend to become broken, probably in some specimens they would be almost or quite wanting.

XII. Magnetic qualities of nickel (supplementary paper)

The present paper is a supplement to one with the same title, by the author and Mr. G. C. Cowan, which was read before the Royal Society on May 17 (p. 325, Suprà ). In that paper experiments were described in which the effects of stress, consisting of longitudinal pull, on the magnetic permeability and retentiveness of nickel had been examined, and it was shown that longitudinal pull had an immense influence in reducing both induced and residual magnetism in nickel. It was, therefore, to be expected (as Sir William Thomson pointed out in his first discussion of the effects of stress on magnetic quality) that longitudinal compression would make nickel more susceptible of magnetisation, and more ready to retain magnetic polarity. Experiments on the magnetisation of nickel under compression have now been carried out under the author’s directions by two of his students, Mr. W. Low and Mr. D. Low, and the results are described below. Further experiments have also been made to investigate the magnetisation of nickel, in very strong magnetic fields, by the method already used for iron by the author and Mr. W. Low, and the results of these are given at the end of this paper. In dealing with the effects of tensile stress on magnetic quality, it is convenient to test the metal in the form of a long wire, long enough to prevent the ends from materially affecting the magnetic field throughout the main part of the length. But in dealing with stress of compression this method of approximating to the condition of endlessness is impracticable. Dr. Hopkinson has shown that a short bar may be brought to a condition of endlessness, suitable for the measurement of its magnetic susceptibility, by sinking its ends in a massive yoke of iron, which affords an easy path for the return of the lines of induction from end to end, outside the bar, and he has made use of this plan in determining the form of magnetisation curves for various samples of iron and steel. This method lends itself well to experiments on the influence of compressive stress, for it is easy to fix the lower end of the bar in the yoke and apply weights directly, or by a lever, to the upper end. The arrangement adopted in the present experiments is shown in fig. 11. The sample under test was a bar of nickel supplied by Messrs. Johnson and Matthey (which was found on analysis to contain 0·75 per cent, of iron). It was 10 cms. long, and was turned to a diameter of 0·656 cms. The yoke was of soft wrought iron, with a cross-section on either side of 67 square cms. The lower end of the bar was supported in the yoke by resting on the end of a screw-bolt; on the upper end a short plunger of wrought iron pressed, and through this the desired stress of compression was applied by means of a lever (fig. 11). The clear length of the sample, within the yoke, was 5 cms. Over this there was wound a magnetising solenoid of 250 turns, inside of which there was a small induction coil wound close to the metal. The magnetisation was determined by reversing the magnetising current while the induction coil was connected to a ballistic galvanometer. To find the residual magnetism the magnetising current was broken after reversal, and the effect of this break was subtracted from half the effect of the reversal. In every case several reversals were made before a measurement was taken; and the process of demagnetising by reversals was resorted to whenever it was necessary to get rid of residual effects of previous magnetisation.

Hughes's Induction Balance

HAVING just made a Hughes's induction balance, I have, in the course of some experiments with it, observed what was new to me, for I have not seen it mentioned in any account of the balance. I take the liberty, therefore, of asking through your columns whether the explanation resolves itself into the difference between paramagnetic and diamagnetic substances. The apertures of my bobbins are 1½ inch in diameter; my primary current is from three Daniell's, and the break is a bent steel spring whose free point just grazes the surface of a mercury cup, so that the merest touch with a finger causes a series of regular breaks. Now, if I place an iron or steel disk, or ring, such as a key-ring, inside the aperture, the telephone sounds loudly if the plane of the disk or ring is at right angles to the plane of the coils; but very very faintly if it is parallel to the plane of the coils. On the other hand, if a disk, or ring, or coil of wire, of any of the diamagnetic metals—copper, brass, zinc, silver, gold, aluminium, lead—be used, the telephone sounds loudly if the plane of the disk or ring he parallel to the plane of the coils; but very faintly, if at all, when it is perpendicular to the plane of the coils. Further, if a short bar of soft iron, or of nickel, be inserted so that the length of the bar is parallel to the plane of the coils, almost no sound is heard; but if it be turned through a right angle so as to be perpendicular to the plane of the coils, the sound is a maximum. Have we in this simple instrument the ready means of distinguishing paramagnetic from diamagnetic substances?

Scientific Serials

Annalen der Physik und Chemie, No. 10.—The loss of electricity by an insulated charged body in rarefied gas in an envelope that has conductive connection with the earth is here stated by Herr Narr to be due to two processes distinct in time and intensity, the first, one of outflow, rapid and intense, the other, one of dispersion, slow and weak. The intensity of the former increases with decreasing density of each of the gases used (CO2 air and H), and also on substituting one gas for the other in the order just given, the density remaining constant. These differences between the gases decrease with the density, and in vacuum fal within the limits of errors of observation. In discussing these results, Herr Narr is led to regard the condensed layer of gas on the conducting system as an insulator, not as a conductor.—Dr. Holz finds that the specific magnetism of magnetic ironstone is the greatest of all magnetic substances hitherto examined. Its maximum permanent magnetism is nearly as great, and partly greater than that of steel as hard as glass. Its permanent magnetism is sooner removed in demagnetisation with the same external forces than that of steel, &c.—Dr. Strouhal enunciates the laws of a mode of sound-production not much studied hitherto, that, viz., of rapid swinging of a rod, a blade, or the like, in air, or the passage of air-currents over strong wires or sharp edges, &c. —Herr Braun contributes a long and (interesting paper on the development of electricity as equivalent of chemical processes.— Herr Koch demonstrates the applicability of the method of determining coefficients of elasticity from the bending of short bars supported at the two ends, the sinking in the middle being measured by means of Newton's interference-bands, and he suggests a more thorough investigation of the elasticity of crystals, by the improved means he describes.—Some remarks on the atomic weight of antimony, with reference to Cooke's recent research, are communicated by Herr Schneider.