b. Odometer similarly held to the great end. Result—Proximad motion of the odometer—that is, again, motion directly from the axis of the egg.
c. Hold the odometer near either side of the egg, one-fifth of the distance from either end. Results—Transverse sinistrad oscillations. The same current may be detected above the egg on the same parallels.
The effects described are given in fig. 17. Then here are, at either end of the egg, two rectilinear currents acting at right angles to each other. Fig. 18 represents the complementary motions to the above, which are obtained by touching the odometer finger with the thumb. A parallel combination of rectilinear motions is produced, but in another way.
The next three figures exemplify the composition of forces necessary to produce the rotatory motion of the odometer.
Figs. 19 and 20 are intended to represent the large ends of two eggs, so placed that the axial currents of the two shall cross at right angles, at a point equidistant, let us say at half an inch exactly, from the end of each egg. If the ring be suspended exactly at the point of meeting of the two forces, it will be driven off in the diagonal, and continue simply to oscillate in the line A B. But if either of the eggs is moved back to double its former distance from the point of intersection of the two forces, the forces will be rendered unequal, and new results will ensue. The two experiments by which the results of this arrangement may be tried are represented in figs. 21, 22, and figs. 23, 24. The longer current is necessarily thereby the weaker of the two in each combination. Accordingly, rotatory motion supervenes in each case instead of diagonal oscillation; and the direction of the rotation is from the stronger towards the weaker current.
Figure 25 represents the various motions which may be elicited by holding the odometer at the sides or over different parts of a horse-shoe magnet. The continued lines in all the diagrams represent the primary motions, the dotted lines their complementary motions.
Figures 26 and 27 represent, in the same way, the primary and secondary oscillations obtainable over the centre of, or parallel to the needle.
Figures 28 and 29 represent the motions displayed by the odometer, when it is held above various points in the interval between two sovereigns, placed upon the table an inch and a half asunder. Compound effects follow, produced by the joint influence of the two bodies.
VI. I will finally describe the phenomena elicited by the odometer from the living human frame, including those which are dependent on difference of sex.