3. Note on a Reptilian Tibia and Humerus (probably of Hylœosaurus), from the Wealden Formation in the Isle of Wight." By J. W. Hulke, Esq., F.R.S., F.G.S. In this communication the author describes two saurian limbbones, remarkable for the great expansion of their articular ends, and the shortness and smallness of their shaft. The features of the tibia are more like those of the tibia of Hylaosaurus than of any other Dinosaur. This resemblance, and the suitability of the humerus to the very massive articular end of the Hylæosaurian scapula, dispose the author to refer the bones to this Saurian. XXXVII. Intelligence and Miscellaneous Articles. ON THE MAGNETIZING-FUNCTION OF TEMPERED STEEL. THE magnetic moment of a magnetized needle may always be regarded as the product of two factors, of which the one expresses the quantity of magnetism contained in the needle (or, if preferred, the power of each pole), while the other factor is equal to the distance of the poles. By the advice of M. Jamin I applied myself to determine these two distinct elements separately, and to study apart the variation of each of them when the conditions of magnetization are changed. The following is the principle of the method employed. It is easy to verify that the magnetic moments y of a series of needles of different lengths 2, magnetized under the same conditions, can be represented by a formula such as provided that their lengths exceed a certain limit l. In all these needles the quantity of magnetism is constant and equal to m, and the distance of the poles from the extremities is also constant and d equal to If we break these needles and take from their middle 2' parts various fragments of lengths exceeding another limit l'<l, their moments y' are represented by the formula the quantity of magnetism is the same as in the mother needle; but the poles are nearer to the extremities, & being always less than d. These facts, almost evident à priori, have been carefully verified by experiment. Suppose now that m and d are to be determined for a given needle. We first ascertain its magnetic moment y; it is then reduced by the removal of a sufficient length from both ends, and the new magnetic moment y' determined. We know * that in ruptureneedles of the same diameter the quantity & is constant, whatever the intensity of the magnetization; its value, known beforehand, is, for instance, 5.5 millims. in needles of 0.553 millim. diameter. "Studies on Magnetism," III., Phil. Mag. March 1875, pp. 188-191. Phil. Mag. S. 4. Vol. 49. No. 325. April 1875. * Z Besides, we can shorten the primitive fragment by successive breakings, and thus fix as many points as we will of the right line represented by equation (2): the quantity of magnetism will be obtained with great exactness. The determination of d is much less precise, since for settling its value we have only one observation, that which refers to the mother needle, and moreover d is always very small. Still, by multiplying observations and taking their means we arrive at satisfactory results. By means of this method I have studied the manner in which the quantity of magnetism and the distance of the poles vary when needles 0-553 millim. in diameter, tempered very hard, are magnetized by being passed through one and the same spiral, and the intensity of the current is varied. Quantities of magnetism.-The average results obtained are represented in the following Table, the numbers in both columns being expressed in arbitrary units. H Several physicists, amongst others Stoletow and Rowland +, have recently applied themselves to the determination of what the former calls the " magnetizing-function" of various sorts of iron or steel; it is the ratio ˊ of the quantity of magnetism H developed either temporarily or permanently in unit volume of the substance taken under the form of a cylinder of infinitesimal transverse dimensions in proportion to its length, to the force F which produces the magnetism by acting in the direction of the axis of the cylinder. The clearest way of representing this function consists in constructing a curve the ordinates of which are the quantities H, and its abscissæ the forces F. At first concave towards the positive ordinates, it afterwards presents a point of inflection and approaches asymptotically towards a parallel to the axis of the abscissa. The numbers contained in the preceding Table are proportional Ibid, August 1873. • Philosophical Magazine, January 1873. to F and H. The curve given by them presents the same general characters as do Stoletow and Rowland's curves, but with more rigid turns, a concavity towards the positive H strongly pronounced for small values of F, an inflection so elongated that for a considerable portion of its extent the curve is indistinguishable from a straight line; in a word, it has the appearance of a broken line with the obtuse angles much rounded: such are the results given by the construction of the new curve. They confirm the facts discovered by entirely different methods in the case of iron, at the same time that they characterize the peculiar consistence of very stiffly tempered steel, and supply an unexpected verification of the theoretic ideas I have put forth elsewhere on the subject*. Finding it impossible to effect absolute measurements, I could do no more than compare Rowland's results with mine, in the manner indicated by the following Table. C is the abscissa at the origin of the tangent to the point of inflection, C' the abscissa of the point where the tangent meets the asymptote to the curve, L the maximum of magnetization. All the ordinates are expressed as functions of C, all the abscissæ as functions of L. The interval from C to C' might be named interval of rapid magnetization. Within these limits, distant 0.973 C, for iron, 1-608 C, for chilled steel, the quantity of magnetism increases from of its maximum value up to nearly for iron and for steel. The determination, in absolute value, of C, C', and the corresponding ordinates would furnish a good comparison of the magnetic powers of different kinds of steel, iron, &c., and at the same time would fix the limits which it would be absurd not to reach, or not economical to exceed, in the intensity of the currents employed for the magnetizing. In a future communication I shall indicate the results regarding the distance of the poles, as well as the changes produced in the quantity of magnetism or in the polar distance when the needle is: passed repeatedly through the magnetizing spiral.-Comptes Rendus de l'Académie des Sciences, vol. lxxx. pp. 650–653. * 64 et seqq. Studies on Magnetism," IV., Phil. Mag. March 1875, p. 199 ON THE DEPENDENCE OF THE COEFFICIENT OF FRICT MOSPHERIC AIR ON TEMPERATURE. BY ALBERT MAYER, CAPTAIN OF ARTILLERY. Of the two hypotheses from which the dynamical the starts, the older gives the coefficient of friction of ga tional to the square root, the newer (Maxwell's) gives it P to the first power of the absolute temperature. From t tions of vibrating disks by the friction of the air, Max experimentally the power 1, O. E. Mayer the power 3 ; ments on currents through capillary tubes O. E. Mayer power, J. Puluj the power, of the absolute temperat For the more certain determination of the ratio, exper currents through four capillaries of glass and one of undertaken; and together with the temperature of the r of boiling water, congealing paraffin, and a mixture of salt were employed. A first series of experiments, less accu carried out with the difference of pressure variable; a se siderably more exact, with the difference constant. The results of the two series agree very well, and con of Mayer's experiments in a perfectly satisfactory man the coefficient of friction μ at the temperature t there were According to the first series, μ=0·0001706 (1+0·0027 second μ=0-00016747 (1+0.002 -Kaiserliche Akademie der Wissenschaften in Wien, Sitzung naturw. Classe, Feb. 4, 1875. ON CAMACHO'S NEW ELECTROMAGNET. To the Editors of the Philosophical Magazine and Jour General Post March 2, 1 Camacho's concentric-tube electromagnet seems to be i in principle with one lent me when I lived in Mancheste 1852, by the late Richard Roberts, so well known in co with spinning-machinery. His electromagnet was an iron cube sawn nearly throu number of parallel cuts, crossed at right angles by other cut to form a series of cores connected at one end. Each of the cores was wrapped with wire, forming a s electromagnets, connected by a common breech piece in connexion with all the cores. This arrangement was very powerful for its size; I regret have no note of its performance. Yours faithfully, |
