Feb,^, 1888] 



NATURE 



345 



they may co-operate properly, they must represent posi- 

 tive and negative electricity alternately. If they then 

 rotate alternately in opposite directions, all is well, and 

 the electrical circulation or rotation in the field is all in 

 one direction. Each wheel gears into and turns the next, 

 and so the spin gets propagated right away through the 

 medium, at a speed depending on the elasticity and 

 density concerned in such disturbances. 



It is not convenient at the present stage to ask the 

 question whether the wheels represent atoms of matter 

 or merely electricity. It may be that each atom is 

 electrostatically charged and itself rotates, in which case 

 it would carry its charge round with it, and thereby con- 

 stitute the desired molecular current. 



The apparent inertia of electricity would thus be 

 explained simply enough, as really the inertia of the 

 spinning atoms themselves ; and the absence of any 

 moment of momentum in an electro-magnet as tested 

 mechanically would be equally explained by the simul- 

 taneous opposite rotation of adjacent atoms. . A question 

 may arise as to why the opposite molecules should have 

 exactly equal opposite inertitC, as they have, else a fluid 

 magnetized medium would bodily rotate ; and there nay 

 be other difficulties connected with a bodily rotation of 

 electrostatically charged molecules : it is merely a possi- 

 bility upon which stress must not be laid till it has been 

 proved able to bear it. For our present purpose a spin 

 of the electricity inside each atom, or even independently 



row slip, then the direct and return circuit are on opposite 

 sides of the row. But a large area of any shape with nc 

 slip inside it may be inclosed by a line of slip, and this 

 gives us a circuit of any shape, but always closed. Under- 

 stand : one is not here thinking of a current as analogous 

 to a locomotion of the wheels — their axes may be quite 

 stationary, — the slip contemplated is that of one rim on 

 another. 



Imagine all the wheels inside the empty contour of 

 Fig. 38 to be rotating, the positive clockwise, the negative 

 counter clockwise, and let all those outside the contour 

 be either stationary or rotating at a different rate or in 



Fig. 37. — Portion of a magnetic field. Aoother mode of drawing Fig. 36. 



of any atoms, is quite sufficient. Besides, since magnetic 

 induction can spread through a vacuum quite easily, the 

 wheel-work has to be largely independent of material 

 atoms. 



If any difficulty is felt concerning the void spaces in 

 Fig. 36 it is only necessary to draw it like Fig. 37, which 

 does every bit as well, and reduces the difficulty to any 

 desired minimum. 



Ri'.presentation of an Electric Current. 



Now notice that in a medium so constituted and mag- 

 netized — that is, with all the wheel-work revolving properly 

 — there is nothing of the nature of an electric current pro- 

 ceeding in any direction whatever. For, at every point 

 of contact of two wheels the positive and negative elec- 

 tricities are going at the same rate in the same direction ; 

 and this is no current at all. Only when positive is going 

 one way and negative going the opposite way, or standing 

 still, or at least going at a different rate, can there be any 

 advance of electricity or anything of the nature of a 

 current. 



A current is nevertheless easily able to be represented : 

 for it only needs the wheels to gear imperfectly and to 

 work with slip. At any such slipping-place the positive 

 is going faster than the negative, or vice versa, and so 

 there is a current there. A line of slip among the wheels 

 corresponds therefore to a linear current ; and, if one 

 thinks of it, it is quite plain that such a line of slip must 

 always have a closed contour. For, if only one wheel 

 slip, then the circuit is limited to its circumference ; if a 



Fig. 38.— Diagram of a peripheral current partitioned off frjm surrounding 

 medium by a perfect conductor, which transmits no motion, and there- 

 fore acts as a perfect magnetic screen. 



an opposite direction ; then the boundary of the inside 

 region is a line of slip along which the positive rims are 

 all travelling clockwise, and the negative rims the other 

 way, and hence it represents a clockwise positive current. 

 But it may be said that the spin inside the contour, if 

 maintained, must sooner or later rotate the wheels outside 

 as fast as themselves, and then all slip will cease. Yes, 

 that is so, unless there is a complete breach of connection 

 at the contour, as in Fig. 38 there is. If the outer region 

 has any sort of connection with the inner one the slip at 

 its boundary can only be temporary, lasting during the 

 era of acceleration. 



Distinction between a Dielectric and a Metal, as affected 

 by a spreading Magnetic Field. 



In a dielectric the connection between the atoms is 

 definite and perfect. If one rotates, the next must rotate 

 too ; there is no slip between the geared surfaces ; it 

 is a case of cogged wheels. A conduction-current is 

 impossible. 



But in a metallic conductor the gearing is imperfect ; it 

 is a case of friction-gearing with more or less lubrication 

 and slip, so that turning one wheel only starts the next 

 gradually— it may be very quickly, but not instantaneously 

 — and there is a motion of a positive rim incompletely 

 compensated by an equal similar motion of a negative 

 rim while getting up speed ; in other words, there is a 

 momentary electric current, lasting till the wheels have 

 fairly started. 



In a perfect conductor the gearing is absent ; the lubri- 



j cation is so perfect that all the atoms are quite free of one 



another, and accordingly a spin ceases to be transmitted 



into such a medium at all. The only possible current in 



a perfect conductor is a skin-deep phenomenon. 



A magnetized medium of whatever sort is thus to be 

 regarded as full of spinning wheels, the positive rotating 

 one way and the negative the other way. If the medium 

 is not magnetized, but only magnetic — i.e. capable of 

 being magnetized — it may be thought of either as having 

 its wheels stationary, or as having them facing all ways at 

 random ; the latter being probably the truer, the former 

 the easier, representation, at least to begin with. 



