PHYSICS. 607 



angle is small. The same edge produces complementary polarizations. 

 (C. B., March, 1883, xcvi, 697.) 



ELECTRICITY. 



1. Magnetism. 



Hughes has presented to the Eoyal Society a theory of magnetism 

 based on new experimental researches. He maintains (1) that each 

 molecule of a piece of iron, steel or other magnetic metal is a separate 

 and independent magnet, having its two poles and distribution of mag- 

 netic polarity exactly the same as its total evident magnetism when 

 noticed upon a steel bar magnet ; (2) that each molecule or its polarity 

 can be rotated in either direction upon its axis by torsion, stress, or by 

 physical forces such as magnetism and electricity; (3) that the inherent 

 polarity or magnetism of each molecule is a constant quantity like 

 gravity, and can neither be increased or destroyed; (4) that when we 

 have external neutrality or no apparent magnetism, the molecules or 

 their polarities arrange themselves so as to satisfy their mutual attrac- 

 tion by the shortest path, and thus form a complete closed circuit of 

 attraction ; (5) that when magnetism becomes evident, the molecules 

 or their polarities have all rotated symmetrically in a given direction, 

 producing a north pole in the piece of steel if rotated in one direc- 

 tion, and a south pole if rotated in the other. The arrangement here 

 is still symmetrical, but the circles of attraction are completed only 

 through an external armature joining both poles. (Nature, February, 

 1883, xxvn, 354.) 



Wassmuth has shown that the moment of a milligram of iron sub- 

 mitted to a magnetic force, depends upon its temperature and the press- 

 ure to which it is exposed. A diminution of pressure, a rise of tem- 

 perature affect the moment oppositely. Compression evolves nearly the 

 same amount of heat whether the iron be magnetized or not. Iron, 

 therefore, subjected in a vacuum to a feeble magnetic force should be 

 cooled. It would heat, on the contrary, under the atmospheric pressure 

 and the action of a more powerful magnetization. (J. Phys., April, 

 1883, II, II, 194.) 



Bosanquet has proposed the term "magnetomotive force" as the ana- 

 logue of electromotive force; a difference of magnetic potential. He 

 concludes that the magnetic induction of a permanent magnet may be 

 supposed to be produced by a magnet' motive force derived from per- 

 manent amperian currents acting through the resistance of the steel. 

 (Phil. Mag., March, 1883, T, xv, 205.) 



Stefan has observed that if a magnet oscillating under the action of 

 the earth be inclosed within a hollow cylinder of iron, and the diminu- 

 tion which the horizontal component undergoes under these circum- 

 stances be measured, it will be found to equal nine-tenths of the whole 

 value. If a solenoid be placed in a magnetic field, currents may be 



