644 PHYSICS, PROGRESS OF, IN 1892. 



PHYSIOLOGY. 



tions of this nature, since the variation of mag- 

 netic intensity may be too gradual to affect it, 

 as shown inVan Rysselberghe's device for using 

 the same circuit for telegraph and telephone. 



Change of Volume by Magnetization. Knott 

 and Shaud (Edinburgh Royal Society, May 16) 

 find that when an iron tube is magnetized its 

 internal volume is slightly increased in weak 

 fields, but as the field grows stronger it passes 

 through a maximum, then decreases, vanishes, 

 and then changes sign. This cycle is several 

 times repeated, implying a transverse linear 

 dilatation, in general opposite in sign to the well- 

 known longitudinal dilatation. Shelford Bid- 

 well (London Royal Society, May 19) finds 

 that in an iron wire carrying a current the max- 

 imum magnetic elongation is greater, and the 

 retraction in strong fields is less, when no cur- 

 rent passes. The effect of a current is opposite 

 to that of tension. The magnetic retraction of 

 nickel and cobalt, however, is not sensibly af- 

 fected by the passage of a current, though it is 

 modified by tension. 



Magnetization by Passage of a Current. Prof. 

 G. G. Knott (Edinburgh Royal Society, Jan. 18) 

 uses iron tubes for experiments on this phenom- 

 enon, and measures the circular magnetization 

 produced by the induction current in a wire coil 

 wound longitudinally. When the tube was mag- 

 netized by an axial current through a copper 

 wire threading it, or by a sectional current from 

 end to end of the tube itself, the induction was 

 found to be 7 per cent, greater than that required 

 by theory, which, since a current through iron 

 does not increase its permeability to inductive 

 forces perpendicular to the current, shows that 

 the theory must be faulty. 



Increase of Current in a Circuit having Large 

 Electro-magnetic Inertia. Thomas Grey (London 

 Royal Society, May 19) finds that to produce any 

 given percentage of the maximum strength in 

 such a circuit there is always a particular E. M. 

 F. which takes the maximum time. By succes- 

 sive reversals of E. M. F. it can be shown that 

 several minutes may be required for the magnet- 

 ism to be lost. 



Permanent Magnet. W. Hibbert (" Philo- 

 sophical Magazine," March) has constructed a 

 strong bar magnet, one end of which is hemi- 

 spherical, with a pole piece of soft iron, while on 

 the other is a soft iron disk forming the cover of 

 this hemispherical cup. The cover is separated 

 from the edges of the hemisphere by a space -^ 

 inch wide, within which is a helix. This magnet 

 showed no evidence of decay in seven months. 



Lamellar Magnet. Regnier and Parrot (Paris 

 Academy of Sciences, Aug. 8) have constructed 

 a magnet of alternate transverse lamellae of a 

 conducting metal and a magnetic metal, and find 

 that it has a high inductive efficiency. 



Magnetic Curve Tracer. Prof. Ewing, in a 

 lecture before the British Association at Edin- 

 burgh, exhibited a machine of this name, con- 

 sisting essentially of two wires, which move a 

 mirror, one proportionallj to the magnetizing 

 current and the other proportionally to the ac- 

 quired magnetism, thus causing a spot of re- 

 flected light to describe a complex characteristic 

 curve. 



Schiseophone. De Place (Paris Academy, Oct. 

 24) has given this name to a magnetic device for 



detecting flaws in steel. The steel being tapped 

 regularly by a rod attached to a microphone pro- 

 duces characteristic sounds in a telephone in an 

 adjoining room. The variation of sound when a 

 flaw is present enables it to be detected at once. 



Displacements of a Floating Magnet by a Cur- 

 rent. C. Decharme (Paris Academy of Sciences, 

 Oct. 31) finds that if a light magnetic needle be 

 floated on a bath of pure mercury into which 

 electrodes are dipped in different places, the 

 needle, striving to take up its equilibrium posi- 

 tion, and being prevented from doing so at once 

 by the difficulty of motion sidewise, will go 

 through a curious series of movements. If, for 

 instance, the current cross the mercury perpen- 

 dicularly to the needle, the negative current pole 

 being to the left of the south-seeking magnetic 

 pole, the needle will move away parallel to itself, 

 turn round, and come back to its normal posi- 

 tion. 



Electro-magnetic Induction. G. T. Walker 

 (London Royal Society, Dec. 10) finds that when 

 a sheet of copper is so placed as to half cover an 

 alternating magnetic pole, and on this, near the 

 pole, is laid a hollow copper sphere, the electro- 

 magnetic action produces a couple which spins 

 the sphere rapidly. Mr. Walker has succeeded 

 in explaining the phenomenon mathematically. 



PHYSIOLOGY. Respiration. The experi- 

 ments of H. C. Wood and David Cerna, of the 

 University of Pennsylvania, on the effects of 

 drugs and other agencies upon the respiratory 

 movements, were based on the principle that not 

 rapid breathing which may coexist with very 

 little movement of air but the increase of the 

 amount of air breathed in and out of the lungs 

 affords the criterion of a respiratory stimulant. 

 The experiments were performed by connecting 

 the trachea of the animal with a tube, which in 

 turn was connected with two ordinary mercurial 

 valves, one of which allowed the air to enter, the 

 other to escape, the mercurial valve of expira- 

 tion being in turn connected with an India-rub- 

 ber bag or reservoir, from which the air was 

 drawn by means of a suction pump. The record 

 of experiments upon the dog, which usually 

 cools itself by rapidly breathing, shows that 

 heat has an enormous effect upon the respira- 

 tion in narcotism. During narcotism the rectal 

 temperature of the subject had fallen 1-03 0. 

 below the norm ; when by means of external 

 heat the rectal temperature was raised about 

 1 above the norm, the respiratory rate was more 

 than doubled, and the movement of air in the 

 chest increased from 0'15 cubic foot per min- 

 ute to 0'38 cubic foot. In another case, when 

 the rectal temperature was put up 10 above 

 the norm, the air movement rose to nearly 5 

 above the normal amount. It is thus demon- 

 strated that the stimulating effect of heat upon 

 the respiratory centers is as great in the nar- 

 cotized as in the normal animal; and the ex- 

 periments explain the way in which heat pro- 

 tracts or even saves life during narcotism, and 

 enforce the necessity, by means of the hot-water 

 bath or bed, of overheating the human body 

 when respiratory paralysis from some narcotic 

 agent is threatened. Chloral was proved to be 

 a respiratory depressant, producing a marked 

 reduction in the respiratory -movement of the 

 air. Morphine also acted as a depressant, pro- 



