PHYSICS. 475 



Bosanqiiet has tested experimentally the idea of a repulsion between 

 magnetic lines of force, by the use of rings magnetized by means of a 

 continuous wire uniformly wound around tliem, and lias shown that they 

 present no external magnetic action even though they may be the seat 

 of closed circuits of magnetic lines of force of very great intensity. 

 Since we may suppose the ring divided into a number of separate rings, 

 each containing lines of force, and since such rings will be wholly with- 

 out action on one another, it follows that if such similar rings be placed 

 parallel and close to each other they do not repel each other, as they 

 should do if there existed a repulsion between parallel lines of force. 

 {Phil. Mag., December, 1884, V, xviii, 494.) 



McGee has described a novel magnetic engine, based on the diminu- 

 tion in the magnetism of iron by heat. It consists of a ring 13*="" in 

 diameter, made up of one or more turns of iron wire and supjiorted on 

 radial arms so as to revolve about a vertical axis. Near it, and with 

 its axis in a radial direction, is a permanent bar-magnet. If now the 

 ring of wire be heated to bright redness on one side or the other of the 

 magnet, this magnet exerts a stronger attraction upon the wire on the 

 oi)positeor cooler side than upon the heated side, and the ring revolves. 

 By means of a pulley and string on the axis, using a powerful electro- 

 magnet, a weight of six grams was raised SC^"" in six minutes. The 

 source of energy is of course the gas-burner employed. {Science, iii, 

 274, March, 1884.) 



Stracciati has studied the currents i^roduced in iron by its demag- 

 netization,,and their influence upon the rapidity of this demagnetization, 

 using for these experiments the method of Felici. He concludes that 

 the rapidity with which the magnetism of a mass of iron disappears 

 when the magnetizing force ceases, diminishes at first rapidly, when 

 this force increases, but appears finally to tend toward a constant value 5 

 and that this velocity in the case of a bundle of iron wires separated by 

 silk from each other diminishes notably when the mass is rendered a 

 continuous conductor, as by plunging it in a bath of mercury. {J. Phys., 

 December, 1884, II, iii, 552.) 



Trowbridge and Hill have made an elaborate investigation of the heat 

 ])roduced in iron and steel by reversals of magnetization. Their con- 

 clusions are as follows: (1) The heat developed is probably due to in- 

 duction currents and not to molecular vibrations ; (2) the heating is 

 confined to the s^lrface until equalized by conduction; (3) the musical 

 note emitted is the note of the coil, due to the number of reversals of 

 the machine, and is merely strengthened by the metallic core; and (4) 

 these experiments confirm what has long been known on the effect of 

 vibrations and shocks on the magnetic condition of iron and steel. 

 {Am. J. Sci., Jiinnary, 1884, HI, xxvii, 58.) 



Bakmetieft", who has also investigated these phenomena, arrives at 

 the conclusion that magnetism by itself produces variations of tempera- 

 ture in magnetized bodies, and that this magnetic heat is equal to the 



