p. 1

[Scrap Book] Am. Jour. Science
No. 53—May—1875
see page 400

Chemistry and Physics.

desired until the length becomes small compared with the diameter. The law for changes in the diameter and the effect of a fracture parallel to the axis were also studied. Finally, on the ground of the peculiar facts examined in this memoir, as well as the whole of the known facts, he concludes that the present theories of magnetism are insufficient to explain the peculiarities of the temporary magnetization of steel, and suggests that in regard to the magnetic properties of its elements this substance must be considered a heterogeneous mass.—Phil. Mag. xlix, 81, 186.

9. Frictional Electricity.—M. Rossetti has made a careful study of the current developed by a Holtz machine and shown that it follows the laws of a galvanic battery. The machine was turned by a weight, and the work done measured when charged and discharged. The current was determined by a galvanometer and the resistance by four long fine tubes filled with distilled water. The current is nearly proportional to the speed, but increases a little more rapidly than the latter. The ratio of the two alters with the amount of moisture in the air, so that to produce a given current the machine must be driven faster in wet weather, although the work required is less than when the air is dry. The economy, therefore, is greater on wet than on dry days. A Holtz machine resembles a galvanic battery, having an electromotive force and interior resistance which are constant as long as the velocity and moisture are constant. The electromotive force is invariable for a given degree of moisture whatever the velocity, while with a given velocity it diminishes as the moisture increases. The interior resistance on the other hand is independent of the moisture and diminishes more rapidly than the velocity increases. In the actual instrument employed, when the moisture was 69 the electromotive force equaled 41,000 volts, while with the moisture 35 it equaled 57,000 volts. The resistance with a velocity of eight turns per second was 540,000 ohms, and with a velocity of two turns 2,680,000,000 ohms. The current follows the law of Ohm, consequently if very large exterior resistances are employed, the strength of the current gives the mechanical equivalent of heat. The mean of seventeen experiments gave as a result the number 428, which agrees very closely with the commonly received value.—Ann de Chim et Phys. iv, 214. E.C.P.

10. Chemical Sub-section in the American Association for the Advancement of Science,—This sub-section of the American Association was organized at the Hartford meeting in August last. It is called the "Sub-section of Chemistry, Chemical Physics, Chemical Technology, Mineralogy and Metallurgy," and all persons interested in applied as well as in pure chemistry will be welcome at Detroit, where the next session to be held, in August of this year. We make this statement very willingly at the request of Prof. F.W. Clarke, of Cincinnati University, who is the secretary of this section, and who is making active exertions to secure a large gathering of chemists on that occasion. Prof. S.W. Johnson, of Yale College, is chairman-elect of this section.