II. Analysis of the forces, or currents conducing to, or implicated in the movements of the odometer just described.
It has been said that the above movements manifest themselves when the odometer is held over the centre of the Od-subject. Let us now examine the consequences of holding the odometer extra-marginally to, or beyond the edge of, the Od-subject.
a. Let the odometer be held a quarter of an inch away from, and over each cardinal point of a sovereign, or zinc circular disc, in succession. Result—Held near the distal point, its motion is proximad. Held near the proximal point, its motion is proximad. Held near the dextral point, its motion is sinistrad. Held near the sinistral point, its motion is sinistrad. (See fig. 3.)
But the first two impulses thus attained correspond with the direction of the primary oscillations of the odometer, the last two with its complementary oscillations; and if the odometer be held now over different points in succession of the two diametral lines, suspended, of course, by the finger alone over the first series of points, and by the finger touched by the thumb over the second, it will be found that the primary oscillations originated over every point of the longitudinal diameter of the zinc disc are proximad; and that those obtainable over any part of the transverse diameter of the zinc disc are sinistrad.
Then the forces or currents are made manifest by which the two sets of oscillations are produced; and the marvel of the prompt substitution of one for the other is at an end; for it is evident that these two forces, whether produced or only revealed by the presence of the odometer, co-exist; and that the changed Od-relations of the experimenter to the odometer, (effected by disjoining the thumb from, or joining it to, the forefinger,) simply act by giving temporary predominance to one of the two co-existent currents.
If these experiments be made at the edge of the copper disc, they elicit opposite but parallel results. (See fig. 4.) They evince the existence of two currents, one dextrad, the other sinistrad, from which the same conclusions may be deduced.
It is important to notice, that in all this class of the experiments, the distad and dextrad currents are manifested in combination; and in like manner the proximad and sinistrad.
This combination is further exemplified in the next experiment, which I shall describe.