It is, however, doubtful whether these currents traverse the whole disc. For if the experiment is made of following each upon the disc, their influence disappears at less than a quarter of the diameter, where the odometer is found to obey on the zinc disc the proximad current, on the copper disc the dextrad current. Or, probably, these currents are the simple expression of the action of two equal forces moving the body operated on by them (at right angles to each other) in the diagonal. These effects thus form a remarkable contrast with the results given in figs. 7 and 8, wherein rotatory movements are manifested; and they seem to show that an essential element in these rotatory movements is, that one of the two currents acting on the odometer must, in the latter case, be of superior force to the other. _e._ Repeat the last experiments versed, or with the thumb applied to the forefinger. _Results_—(see figs. 11 and 12)—Tangential forces are developed, the directions of which are opposite, as obtained over the zinc and over the copper discs. _f._ Repeat the extra-marginal trials of the odometer in all the halves of the inter-cardinal spaces, both with the zinc and with the copper discs. (See figs. 13 and 14.) _Result_—A complicated series of rotatory movements, eight for each disc; four in each case showing clock-rotation—four versed rotation—but opposite in the corresponding spaces of the two discs. On applying the thumb to the odometer finger, the rotations become exactly inverted so that, in that case; fig. 14 represents what is now manifested in the zinc disc, fig. 13 what is now manifested in the copper disc. III. Motions of the odometer obtained over the same class of substances, when of irregular figure and unequal thickness. _a._ Let the odometer be held over the middle of a line of four sovereigns disposed either longitudinally, transversely, or obliquely. _Result_—Long oscillations over the axis of the line of sovereigns. But the oscillations are not of equal length. At one end of the line they extend to the edge of the fourth sovereign. At the other, they pass an inch beyond it. _b._ Repeat the experiment, touching the odometer-finger with the right thumb. _Result_—Axial oscillations as before, and unequal as before, but in the contrary direction. _c._ Dispose four sovereigns in a line; then place two others upon any one of the four, and hold the odometer over the table at three inches to one side of the middle of the line. _Result_—The odometer swings in each instance towards that sovereign on which the two additional are placed—but unequally. We will suppose that it has swung with sufficient strength to reach the disc of the loaded sovereign,—the oscillation in the contrary direction is but two inches in length.