660 PHYSICS, PROGRESS OF, IN 1894. 



PHYSIOLOGY. 



iron, according to whether the magnetizing cur- 

 rent is turned on suddenly or applied gradually. 

 In the latter case it made a difference whether 

 the current reached its final stage by increase 

 from a lower value or by decrease from a higher. 

 If the current be gradually increased a point of 

 maximum elongation is reached. A further in- 

 crease of current causes a decrease of elongation, 

 but a gradual decrease results in a still greater 

 elongation. The expansion is a function of the 

 ratio between the diameter and length of the 

 bar, varying approximately as the square root of 

 this ratio, and also directly as the permeability. 

 The measurements were made with an inter- 

 ferential refractometer (" Annual Cyclopedia," 

 1893, p. 621) that could read to the millionth of 

 an inch. II. Nagaoka (ibid., December) finds that 

 the elongation in iron and the contraction in 

 nickel, due to magnetization, is accompanied by 

 hysteresis, so that when a wire has been mag- 

 netized it can not be brought to its original 

 length simply by reversing the magnetic field. 



Hysteresis. C. P. Steinmetz (" Electrical 

 World," New York, June 9) calls attention to 

 the fact that hysteresis and magnetic friction 

 have no direct relation, although they are equal 

 when there is no external source or expenditure 

 of energy. If there is external transformation 

 of energy, as in revolving machinery, disappear- 

 ance of hysteresis means only that the energy of 

 molecular friction is supplied from a different 

 source. Prof. Ewing and Miss Klaasen (" Elec- 

 trician," London, May 11) find that when a rap- 

 idly alternating current is passed through one 

 of a pair of coils, the magnetizing effect of a 

 steady current through the other is nearly inde- 

 pendent of the previous history of the iron, hys- 

 teresis being almost absent. The effect is ex- 

 plained by the molecular jarring effected by the 

 alternating current. F. G. Baily (British Asso- 

 ciation, 1894) has confirmed experimentally 

 Ewing's deduction from his theory, that in a 

 rotating field the hysteresis should diminish at a 

 high induction. 



Induction. Ernst Lecher (Vienna "Berichte," 

 July 12) finds that if a magnet is divided equato- 

 rially into halves that can rotate separately it is 

 possible to obtain from the two ends by suitable 

 spring contacts an induction current that can 

 not be due to a cutting of the rotating lines of 

 force in the short spring contacts. The current 

 may be explained on the supposition once enter- 

 tained by Faraday, but later abandoned by him, 

 that the rotating magnet cuts its own fixed lines 

 of force and thus has an electro-motive action. 



Electrical Resistance, as affected by Magnet- 

 ixm. Du Bois (Berlin Physical Society, June 1) 

 has investigated the changes of resistance of a 

 bismuth spiral in a powerful magnetic field. In 

 a field of 38,000 C. G. S. units the resistance is 3 

 times that in one of zero intensity. In weak 

 fields a rise of temperature increases the resist- 

 ance ; in stronger fields the effect is less, and it 

 vanishes in a field of 7,000 C. G. S. In still 

 stronger fields the resistance of a warm spiral is 

 less than that of a cold one. The temperatures 

 observed were between and 25 C. 



titri'iujtli of an Electro-magnet. S. P. Thomp- 

 son and M. Walker (London Physical Society, 

 April 27) find that when the magnetic induction 

 does not exceed 4,000 C. G. S. units the pull 



exerted by a laminated electro-magnet on its 

 armature is the same, whether it be excited by 

 a continuous or by an alternating current of 

 equal strength. For higher inductions the con- 

 tinuous current gives slightly greater force. 



Free Magnetism. Curie (" Journal de Phy- 

 sique," September), employing his method of 

 physical symmetry (see below), shows that there 

 is nothing absurd or inconsistent with facts in 

 the supposition that magnetic conductibility and 

 free magnetism may exist. 



Magnetic Shields. Prof. A. W. Riicker (Lon- 

 don Physical Society, Nov. 24, 1893) finds by 

 theoretical considerations, which are confirmed 

 by experiment, that for a small thickness a sin- 

 gle continuous shield gives the best results, while 

 for a greater thickness two shells separated by 

 an air gap are better. When the permeability 

 of the substance is high, the best shielding is 

 obtained when the radii of the bounding sur- 

 faces of the shells are in geometrical progression. 



Miscellany. /Standards of Measurement. 

 C. E. Guillaume (" Journal de Physique," May) 

 has carefully investigated metals suitable for the 

 construction of standards of length. The con- 

 ditions to be fulfilled are reasonable price, hard- 

 ness, and good polish, constancy of length at a 

 given temperature, power of resisting moisture 

 and ordinary chemicals, and, for lai'ge rules, a 

 high modulus of elasticity. Iridio-platinum 

 fulfills all expectations in regard to durability, 

 but the cost of a metre rule would be about 

 $2,000. The condition of constancy excludes all 

 zinc alloys. Ferro-nickel is acted on by water. 

 Phosphor and aluminum bronzes are blackened 

 by steam, and white bronze (nickel 35 parts, 

 copper 65 parts) is attacked by traces of sulphur 

 or chlorine. Nickel is, on the whole, the most 

 suitable metal, but it is difficult to obtain com- 

 mercially free from small punctures, and until 

 this difficulty is surmounted an alloy of equal 

 parts of nickel and copper may do good service 

 at moderate cost. 



Symmetry in Physical Phenomena. P. Curie 

 (' Journal de Physique," September) has made 

 an exhaustive classification of the different 

 forms of symmetry with special reference to 

 physics, and shows how it may be used as an aid 

 to physical investigation. 



Physical Nomenclature. Fitzgerald and Trou- 

 ton ("Nature," Dec. 14, 1893) recommend the 

 extension to general physics of Heaviside's elec- 

 tro-magnetic system of nomenclature. This uses 

 the termination tion for the phenomenon, aure 

 for its amount, and ivity for its coefficient. 

 Thus we should have sets of words like absorp- 

 tion, absorbance, absorbivity; diffusion, diffu- 

 sance, diffusivity ; reflection, reflectance, reflec- 

 tivity ; rotation, rotatance, rotativity. " Inert- 

 ance" would correspond to what we now call 

 "mass," and " inertivity " to "density." 



PHYSIOLOGY. Respiration. An investi- 

 gation of the respiratory exchange in eggs has 

 been made by M. S. Pembrey, M. II. Gordon, 

 arid R. Warren as a part of the research upon 

 the power in virtue of which warm-blooded 

 animals are able to vary their production of 

 heat according to the varying temperature of 

 their surroundings. The authors finfl that the 

 developing chick during the greater part of the 

 period of incubation responds to changes of ex- 



