PHYSICS, PROGRESS OF, IN 1890. 



719 



Lightning. Von Lepel has succeeded in imi- 

 tating globular lightning with an influence ma- 

 chine by holding two thin brass points that are 

 connected with the poles at the proper distances 

 from opposite sides of an insulated plate of mica, 

 ebonite, or glass. Small red, luminous balls ap- 

 pear, sometimes moving about now quickly, 

 now slowly sometimes standing still. A slight 

 air current causes the spherules to disappear with 

 a hiss. Small particles of liquid or dust appear 

 to carry the light. The phenomena are due to 

 weak tension ; higher potential gives rise to a 

 spark discharge. 



Action of -Flames. The British Association 

 committee that was appointed to investigate the 

 subject of the discharge of electrified bodies by 

 flames finds (Newcastle, 1889) that contact is 

 not necessary, and that the discharge is due to a 

 molecular action that moves faster than light. 



Nerve Electricity. Herr Taschenoff (PfliigerV 

 " Archiv.") finds that an electric current is pro- 

 duced in the skin by mental excitation. He ap- 

 plied clay electrodes to various parts of the body, 

 and after compensating the normal current noted 

 the effect of mental stimulus. Tickling caused 

 a deflection, and so did hot water, cold, a prick, 

 sound, light, taste, and odors. Imagination also 

 produced an effect, and an expectant state of 

 mind was accompanied by irregular oscillation 

 of the galvanometer. 



Magnetism. Its Nature. Prof. J. A. Ewing 

 (London Royal Society, June 19) grouped near 

 one another a large number of small pivoted 

 magnets, and studied their configuration and 

 the manner in which it yields to external mag- 

 netic force. The results do not support the the- 

 ory that the molecules in an unmagnetized sub- 

 stance form closed chains, but lead to the con- 

 clusion that it is not necessary to assume any 

 arbitary restraint. J. Hopkinson, in an address 

 before the Institute of Electrical Engineers (Jan. 

 9). sums up recent discoveries in magnetism. He 

 remarks that all magnetic substance, are, com- 

 paratively speaking, enormously magnetic, and 

 that there is no gradation in properties from the 

 magnetic to the non-magnetic. He states that 

 the energy lost in a complete cycle of reversals of 

 magnetism in Whitworth mild steel is 10,000 

 ergs per cubic centimetre ; in oil-hardened steel, 

 100.000; and in tungsten steel, 200,000. The 

 importance of such measurements is seen in the 

 fact that this quantity should be low in dynamo 

 armatures. He says that the magnetic proper- 

 ties of iron are easily destroyed by alloying with 

 a small quantity of manganese and that such an 

 alloy shows no sign of hysteresis (" Annual Cyclo- 

 paedia," 1889, page 702). So far as known, no 

 one has proposed to explain the fundamental 

 anomaly, Why do iron, nickel, and cobalt pos- 

 sess a property not shared by other metals? The 

 rest may be magnetic at very low temperatures, 

 but we have no experimental indication of it. 



The Earth's Magnetism. The results of the 

 "Challenger" expedition of 1882, as regards 

 magnetic observations, have just been discussed. 

 I n general, the earth's magnetic areas, or " poles," 

 seem fixed in position. Near a line from North 

 Cape to Cape Horn are some of the foci of great- 

 est secular change. If the word " red " be used 

 to indicate the north-seeking end of the mag- 

 netic needle and " blue " to signify the opposite, 



there is a blue pole of increasing power in China, 

 a probable decrease of vertical force in the high 

 latitudes of North America, and general change 

 in the relative power of the various poles. There 

 are local magnetic disturbances even in solitary 

 islands. No satisfactory explanation of tin- j.hr 

 nomena has yet been found. 



Magnetism of a Laboratory. The Jefferson 

 Laboratory at Harvard was purposely built with 

 little or no iron, that the magnetic field might 

 be regular. R. W. Willson, who has tested t In- 

 field, however, finds it extremely irregular, 

 steam pipes, a stove, and even the brick in>iru- 

 ment piers, containing enough free magnetism 

 to produce an effect. 



Magnetism of a Railway. Trains on the Cein- 

 ture railway at Paris disturb the bifilar magnet- 

 ometer at Montsouris Observatory, sixty metres 

 distant. The line crosses the magnetic meridian, 

 and the wheel tires thus become magnetized by 

 induction. 



Optical Effects. R. E. J. G. du Bois, of Stras- 

 burg University (" Philosophical Magazine," 

 March), from experiments on Kerr's phenome- 

 non (the rotation of the plane of polarization of 

 a beam reflected from a magnet), concludes that 

 it depends solely on the magnetization that ex- 

 ists immediately behind the mirror surface. At 

 least part of the radiation penetrates below the 

 surface and is there acted on. 



Effect of an Electric Current. C. G. Rente 

 (" Philosophical Magazine," September) finds that 

 a linear current modifies the properties of iron 

 in relation to magnetic after-effect in three ways : 

 1. The total range of magnetic intensity that is 

 produced by a given cyclic variation of magnetic 

 force is less when the current flows ; 2. When a 

 linear current flows, the average intensity of a 

 cycle no longer corresponds to zero polarity, but 

 for a current in one direction it oscillates about a 

 positive, and for one in the other, about a negative 

 value ; 3. A current passing along a wire that is 

 being magnetized, diminishes its susceptibility, 

 but the effect is more pronounced when the wire 

 is acquiring longitudinal polarity in an opposite 

 direction to that in which the current flows. 

 Hence, during any cyclic operation the wire 

 tends to acquire a polarity in the direction of the 

 current. 



Villari Points. These are the values of mag- 

 netic force for which traction produces no 

 change in permeability. H. Tomlinson (London 

 Physical Society, March 21) finds that for an- 

 nealed unstrained iron this critical value of the 

 force decreases as the load increases, and that 

 the Villari point is lower for temporary than for 

 total magnetization. In unstrained nickel the 

 critical value is greater than in iron. In perma- 

 nently strained iron, for forces from 0-03 to 0'3, 

 there is no Villari point ; and the same is true of 

 nickel for minute forces. Iron has two Villari 

 points for higher forces, but with very high ones 

 the wire breaks before the second is reached. 



Diamagnetism. Lodge, commenting on Du- 

 hem's experiments (" Annual Cyclopa-dia," 1889, 

 page 703), says that a perpetual-motion machine 

 could be constructed if they were true. A \vlnrl 

 with a diamagnetic rim might spin near a per- 

 manent magnet so that one side should approach 

 and the other recede from a strong field. For a 

 fast spin the diamagnetism would lag behind the 



