620 SCIENTIFIC RECORD FOR 1885. 



molecular freedom is much diminished, the intramolecular freedom is 

 moderate or high. His figures show a maximum permeability for cast 

 iron of 170 to 250, for malleable cast iron of 700 to 800, of wrought iron 

 of 1,801) to 2,500, and of charcoal iron of 2,900 to 3,000. Hence the infer- 

 ence that ordinary cast iron is wholly unfit for use in dynamo machines. 

 Malleable cast iron is an improvement, but is still very far inferior to 

 wrought iron. {Phil. Mag., January, February, May, October, 1885, Y, 

 XIX, 57, 73, 333, xx, 318.) 



Lippmann has suggested a simple method by which the magnetic po 

 tential of a system of coils may be obtained without calculation. The 

 three coils, a, /?, and y, are so placed at the summits of an equilateral 

 triangle that their axes may form the three sides of an equilateral tri 

 angle, ABC. The variation of magnetic potential due to this system, 

 and taken from B to C, is exactly equal to the product 4;rwi, i being 

 the current strength and n the number of turns in each coil. In order 

 to demonstrate this it is sufficient to remark that if the integral of the 

 magnetic actions exerted by the coil a considered by itself be taken 

 along the contour of the triangle ABC, this integral is exactly equal 

 to 4:7rni, because the contour of the triangle is a closed line. On the 

 other hand, the action exerted by a on the side CA may be replaced by 

 the action of y on the side BC, or the action of a on the side CA may 

 be replaced by the action of /J upon the side BC, so that finally the 

 action of the system of the three coils on the side BC is equal to the 

 sum of the actions exerted by a on the three sides of ABC, i. e., to 

 4:7ini, as above. {J. Phys., October, 1885, II, iv, 448.) 



Ewing has communicated to the Royal Society the results of an ex- 

 tended investigation into magnetic susceptibility, and the influence 

 upon it of various conditions, such as vibration, permanent strain, tem- 

 perature, and the like; the experiments having been made in the labor- 

 atory of the University of Tokio. {Nature, January, 1885, xxxi, 304.) 



Bakmetieff has studied the conditions of the production of heat by 

 alternate magnetizations in a straight wire of iron, measuring the heat 

 by means of a thermo-j unction, so that the greater heating in the middle 

 portions of the straight magnet and the equality of heating in all parts 

 of the annular magnet could be readily observed. The proportionality 

 of the heating to the square of the temporary magnetism was not con- 

 firmed 5 on the contrary, the author advances another law, i. e., that the 

 elevation of temperature of the iron by intermittent magnetization is 

 proportional to the product of the magnetizing force and the magnetic 

 moment. The greatest elevation of temperature observed corresponds 

 to a magnetizing force more than sufficient to saturate the iron; hence 

 the author concludes that it is the increase in the motion of the molec- 

 ular magnets during magnetization which is most important in the 

 production of heat. {J. Soc. Phys. Ghim. Busse, xvi, 81, 257 ; J. Phys., 

 December, 1885, II, iv, 593.) 



