PHYSICS, PROGRESS OF, IN 1894. 



659 



Accumulators. W. M. Stine (" Electrical 

 Engineering," February) states that a serious 

 loss of energy in storage batteries is caused by 

 the recombination of the dissociated atoms into 

 elementary molecular groups as soon as they are 

 set free. 



Alternating Currents. C. J. Rollesson (Amer- 

 ican Association, 1894) has devised a method 

 of recording phonographically the changes in 

 an alternating current. First a record of the 

 curve is produced on the wax cylinder, and then 

 this record is magnified by a multiplying ar- 

 rangement. 



Electric Radiometer. Riccardo Arno (" L'El- 

 ettricista," Rome) has succeeded in obtaining 

 a rotation similar to that of the radiometer by 

 placing an exhausted bulb containing a small 

 windmill in a rotating electrostatic field. The 

 author describes his precautions and reasons for 

 considering that the effect must be due to some 

 action of the rotating field on the molecules of 

 the gas that tends to increase their velocity in 

 the direction of rotation of the field. 



Electro-motive Force. T. H. Blakesley (Lon- 

 don Physical Society, Feb. 23) gives the proof 

 of a new electrical theorem. Premising that, 

 if in any system of conductors two or more 

 modes of disposition of sources of electro-motive 

 force produce in every part of the network the 

 same current, such systems of disposition are 

 called " equivalent systems," he states the theo- 

 rem as follows: "In any system of conductors 

 possessing seats of electro- motive force at any 

 number of points, if any of these sources be sup- 

 posed to move continuously along the various 

 bars of the conducting system, and where a point 

 of junction is encountered, each to become a seat 

 of the same electro-motive force in each of the 

 newly encountered bars, then the disposition at 

 any moment is equivalent to that at any other 

 moment, and therefore to the original' dispo- 

 sition." 



Earth Currents. Lr. Palmieri (' L'Eclairage 

 Electrique "), from several years' study of the 

 earth currents near Vesuvius, finds that when 

 the volcano is quiescent the currents ascend, and 

 when its activity increases they descend. 



Magnetism/ The Magnetic Field. H. Du 

 Bois (Wiedemann's "Annalen," li, p. 587) has 

 produced very strong magnetic fields with ring 

 electro - magnets, by concentrating the flux 

 through properly shaped pole pieces. He con- 

 cludes that it is possible to obtain fields of 

 40,000 centigramme second units with magnets 

 of reasonable size. The assumption that leakage 

 increases as saturation approaches is found to be 

 incorrect. Weber (" Elektrische Zeitung," Nov. 

 1), using a method based on the behavior of 

 liquids in capillary tubes, finds that the field 

 between the poles of powerful electro-magnets 

 ending in truncated cones is not uniform, as has 

 been supposed. A. C. Crehore (American Insti- 

 tute of Electrical Engineers, May 17) has devised 

 a method for recording the variation of a mag- 

 netic field, and so that of the current to which 

 it is due, by change in the refractive power of a 

 material in the field. 



Magnetization. J. Hopkinson and E. Wil- 

 son (London Royal Society, May 31) have inves- 

 tigated the propagation of magnetization in iron 

 as affected by the electric currents in the iron. 



In reversing the magnetizing current of a solid 

 cylindrical electro-magnet the induction does 

 not instantly reverse, and the reversal occurs 

 later at the center of the core than near the sur- 

 face, owing to induced currents in the iron. The 

 authors experimented upon a magnet 4 inches in 

 diameter, forming a closed magnetic circuit, and 

 formed, for part of its length, of an iron core 

 surrounded by two concentric tubes, between 

 which were placed exploring coils of fine copper 

 wire. The currents induced in these coils by 

 reversal of the magnetizing current lasted some- 

 times more than half a minute. With two cylin- 

 ders of different diameters similar events occur, 

 but at times proportional to the squares of the 

 diameters. Ascoli and Lovi (Accademia dei 

 Lincei) find that the radial distribution of mag- 

 netism in long cylinders (50 centimetres) is prac- 

 tically uniform, while in shorter cylinders there 

 is an increase in the induction in passing from 

 the axis outward, which is greater with strong 

 than with weak inducing fields, and is most no- 

 ticeable with cylinders 5 to 10 centimetres long. 

 P. Joubin (Paris Academy of Science, Jan. 8), 

 from comparison of the formulae representing 

 the magnetization of soft iron, in terms of its 

 susceptibility and the strength of the field, with 

 those for solution in fluids, concludes that the 

 two phenomena are analogous, and that magnetic 

 and solutive saturation may be calculated by the 

 same formulas. Circular magnetization has been 

 investigated by I. Klemencic (Vienna " Berichte," 

 July 5), who finds that with soft annealed iron 

 wire the susceptibility circularly about the axis 

 is less then along the axis. If the wire be hard- 

 ened by a stress, the susceptibility diminishes 

 longitudinally more rapidly than circularly, and 

 the behavior of soft iron may even be reversed. 

 The remanent magnetism is greater for circular 

 than for axial magnetization, especially in hard 

 iron and in steel. The same experimenter (Vienna 

 Academy) finds the values obtained for the per- 

 meability of iron when magnetized by rapid elec- 

 trical oscillations agree with those obtained by 

 Raylcigh with very feeble magnetizing forces. 

 This indicates either that the magnetizing force 

 of the oscillations is small, or that the magnet- 

 ization is unable to follow the rapid changes in 

 the force. L. W. Austin (" Physical Review," 

 March-April) finds that the magnetic moment 

 of a permanent magnet, magnetized at ordinary 

 temperatures, becomes slightly greater when its 

 temperature is reduced to that of solid carbon 

 dioxide and ether. This result is in direct con- 

 tradiction to that obtained by Prof. J. Trow- 

 bridge ("American Journal of Science," xxi, 16). 

 P. Curie (Paris Academy of Science, May 21) 

 finds that oxygen, manganese chloride, ferrous 

 sulphate, and palladium follow the law expressed 



by the formula k = , where k is the specific 



constant of magnetization, A a constant, and T 

 the absolute temperature. S. H. Brackett (" Phys- 

 ical Review," November-December), from experi- 

 ments on indium, concludes that this metal has 

 very low permeability but great coercive force, 

 with high intensity of magnetization. 



Elongation due to Magnetization. S. J. 

 Lochner (" Philosophical Magazine," December) 

 finds that, for a given magnetizing field, differ- 

 ent elongations are produced in a bar of soft 



