734 



PHYSICS. 



PHYSIOLOGY. 



increase the average intensity in the direction of 

 the magnetizing force, but also to bring into 

 prominence a relatively high intensity in direc- 

 tions at right angles to it. 



Distribution of Magnetism. This has usually 

 been tested by rods, ellipses, or spheres applied 

 to the magnetic body, but these alter the very 

 thing they are designed to measure. Prof. S. P. 

 Thompson (London Physical Society, March 10) 

 uses a flat coil and a galvanometer. His results 

 show that the perturbations caused by the ,so- 

 called " proof pieces " are very large, sometimes 

 the perturbed field about the point of contact 

 being from four to six times as great as the 

 unperturbed field. 



Propagation of Induced Magnetism in Iron. 

 To ascertain the rate at which this takes place, 

 Fred. T. Trouton (" Nature," Nov. 12) passed an 

 alternating current through a coil placed radi- 

 ally around a ring of soft iron, supposing that 

 the interference of the magnetic waves thus pro- 

 duced would cause magnetic nodes in the ring. 

 These nodes he tried to detect by a shifting coil 

 attached to a telephone. Nodes were at once 

 observed, but they were not due to interference, 

 for the distance between them was unaffected by 

 a change in the rate of alternation of the cur- 

 rent. The effects on opposite sides of the same 

 node, however, were of opposite phase,, just as if 

 interference had been the cause ; but, notwith- 

 standing this, the currents induced on either 

 side of a node are not of opposite sign. Mr. 

 Trouton concludes that the phenomenon depends 

 on some permanent peculiarity, round the ring, 

 that happens to occur regularly; but what this is 

 or how it is caused is yet unknown. 



Magnetism and Light. A. B. Basset (London 

 Royal Society, Jan. 8) has endeavored to explain 

 Kerr's phenomenon (the rotation of the plane of 

 polarization of a ray of polarized light by reflec- 

 tion from the polished end of a magnetic 

 substance) by considerations based on the elec- 

 tro-magnetic theory of light. In metals the 

 phenomenon is complicated by the difficult one 

 of metallic reflection, but it is shown also by some 

 non-metallic magnetic substances, such as solu- 

 tions of certain chemical compounds of iron, and 

 he devotes his attention to these. His explana- 

 tion is developed mathematically from Rowland's 

 assumption that Hall's effect (the production of 

 a cross electromotive force by the passage of a 

 current through a conductor in a magnetic field) 

 holds good in a dielectric. The results agree 

 pretty well with experiment but not entirely. 



Position of Virtual Poles. Thomas H. Blakes- 

 ley (London Physical Society, Nov. 28, 1890) 

 discusses the problem, " given the two virtual 

 poles of a magnet and a straight line intersect- 

 ing at right angles its axis produced, to deter- 

 mine at what point this line is parallel to the 

 field." "The mathematical solution is of scientific 

 interest, because this point can be experimentally 

 determined and the distance of the virtual poles 

 can then be calculated. Blakesley's geometrical 

 solution and his resulting formula are given in 

 " Nature," Dec. 25, 1890. 



Change of Form affecting a Magnetic Field. 

 Prof. A. E. Dolbear, from experiments on a flex- 

 ible magnetic ring, (American Academy of 

 Sciences, Boston, Jan. 14), comes to the follow- 

 ing conclusions : 



1. A change in the form of a magnet causes 

 corresponding change of stress in the field. 



2. Periodic changes in form due to elasticity 

 of form, such as are called sound vibrations, set 

 up similar periodic changes or waves in the mag- 

 netic field. 



3. Such vibrations set up in other magnets 

 similar vibrations, either sympathetic or forced. 



4. These vibrations of the receiving magnet 

 change its field, setting up electric currents in 

 surrounding circuits. 



Prof. Dolbear suggests that all atoms are 

 magnets, so that their vibration must set up 

 electro-magnetic ether waves. A ring magnet is 

 the most perfect form possible, and thus Sir 

 William Thomson's vortex atom theory at once 

 suggests itself to the mind. 



Magnetism and Electrical Oscillations. Con- 

 trary to general belief, Prof. John Trowbridge 

 shows (" American Journal of Sciences," Septem^ 

 ber) that (1) the magnetic permeability of iron 

 wires exercises an important influence on the 

 decay of electric oscillations of high frequency ; 

 (2) probably the time of oscillation in iron wires 

 may be changed ; and (3) therefore a current of 

 high frequency a Leyden-jar discharge, for in- 

 stance magnetizes the iron. 



Magnetic Force due to Steady Currents. Dr. 

 Schuster (" Philosophical Magazine," July) shows 

 that this can Always be expressed in terms of the 

 value of the current at the surface of the con- 

 ductor ; the current within may be unknown, 

 though, of course, it is determined by that on 

 the surface. 



The Earth's Magnetism. Prof. F. H. Bigelow 

 (" American Journal of Science," September) 

 thinks that the permanent magnetism of the 

 earth may be principally due to its orbital motion 

 through the radiant field of sunlight. The 

 rotation of the earth on its axis introduces a 

 modification, and may result in a rotation of the 

 axis of polarization about the axis of figure : or, 

 if the magnetization has already become set in 

 the earth, may cause a succession of secular waves 

 to sweep over it from east to west, as shown in 

 the history of the isogonic lines. 



Diamagnetism. J. Parker (" Philosophical 

 Magazine," August and September) thinks that 

 the theory of diamagnetic polarity is as absurd 

 as it would be to claim that the ascent of a bal- 

 loon is due to " diagravitation." He develops 

 mathematically the theory that diamagnetic 

 effects are really due to the "magnetic pressure of 

 the surrounding medium. To those objectors 

 who assert that in this case we must ascribe 

 magnetic qualities to a vacuum, since diamag- 

 netic phenomena occur in an exhausted receiver, 

 he replies that we can not obtain a perfect vacu- 

 um, and that the residual gas in the best vacu- 

 um we can get is quite sufficient to account for 

 the observed facts. 



PHYSIOLOGY. The physiological researches 

 of the year 1891 have not been marked by any 

 new or striking discoveries, but have indicated a 

 steady advance all along the line. Heidenhain's 

 work on lymph has resulted in showing that the 

 absorption of products of digestion is not merely 

 osmosis ; that the exudation of lymph can not 

 be explained simply as due to diffusion under 

 pressure, but is dependent on the secretory ac- 

 tivity of the endothelial cells in the capillary 



