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.
d. Repeat the experiment, with the thumb applied. Results—Oscillations ensue of the same length, and they are again unequal, but in the contrary direction. Now they do not reach the pile of sovereigns by an inch, but they pass three inches in the opposite direction.
Thus a force is brought into view having this new quality: when the Od-relations of the experimenter are versed, a change ensues, not into motion in a plane transverse to the former one, but the direction of the new motion is simply the opposite of the first, or the odometer appears to be attracted or repelled towards the Od-subject alternately.