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192 SCIENCE PROGRESS 



poles occupying the corners of a regular tetrahedron. The 

 mutual magnetic forces between the Weber element and the 

 outer group determine the range through which the Weber 

 element can turn stably, and when this range is exceeded, it 

 turns irreversibly in a manner involving hysteresis from one 

 position of stability to another. Calculation and experiment 

 combine to show that in this model the strong magnetic forces 

 between the Weber element and separate portions of the outer 

 group make the range of stable deflection very narrow and yet 

 are more or less completely balanced, so that the stability is 

 feeble. This structure has obvious points of similarity with 

 the structures dealt with in the last contribution to this section 

 of " Recent Advances," in which electrons are supposed to 

 be confined to narrow limits near the corners of regular poly- 

 hedra. In particular the Langmuir hypothesis concerning the 

 arrangement of the 26 planetary electrons in the iron atom is 

 that 2 form an inner " stable pair," and the remaining 24 are 

 at the corners of three concentric cubes with common diagonals 

 — an arrangement which could easily be conceived to possess 

 the two elements postulated in Ewing's new model of ferromag- 

 netic induction. 



However, as stated at the outset, the model has been shown 

 by Whittaker to possess the necessary elements to render it a 

 suitable mechanism for " quantum " exchanges of energy 

 between an atom and an electron which encounters it. In his 

 paper Whittaker obtains the equations of motion for a simple 

 " Weber element " consisting of a magnet rotating in a plane 

 round one of its poles as centre, and an electron approaching 

 it from a distance along a line passing through the stationary 

 pole at right angles of the plane of rotation. The approaching 

 electron constitutes an electric current and produces the usual 

 circular magnetic field which will set the magnet (supposed to 

 be at rest initially) in rotation. Now the rotating pole will 

 constitute a " magnetic current " and in its turn produce an 

 electric field whose lines are Hnked with the circular path of 

 the pole in the same way {except for a difference in sense) as the 

 lines of magnetic force are linked with a circular electric current. 

 Furthermore this electric field will oppose the approach of the 

 electron ; this can be seen if attention is paid to the bracketed 

 remark concerning sense in the previous sentence ; indeed, the 

 whole occurrence is an illustration of the Faraday-Lenz rule. 

 If, therefore, the kinetic energy of the electron is insufficient, 

 it is stopped before reaching the atom, all its energy having 

 been communicated to the rotating magnet. Under the 

 influence of the electric force due to the magnetic current (now 

 at its maximum value) the electron begins to recede, and in so 

 doing creates a magnetic field which gradually brings the 



