POSTSCRIPT.
An accident has given me the opportunity of making further additions to this little volume, of which I proceed to avail myself; and, first, by communicating my latest experiments with the divining-ring, July 24.
I. I have stated that, if a fresh egg be placed upon the table, with the small end directed from me—or a crystal, with one definite pole so turned from me—or a bar-magnet, with its northward pole so disposed—and I then suspend the divining-ring half an inch above either of the three so averted ends, and half an inch further off from me, the ring exhibits clock-rotation in each instance. Held in a parallel manner over the opposite ends—that is, half an inch from, and half an inch higher than, the same—the ring exhibits versed-rotation. If the three Od-subjects be moved round, so that their hitherto distal ends point to the right, or if they be further turned, so as to bring the previously distal ends now to point directly towards me, the ring continues to exhibit exactly the same motions as in the first instance.
If, these objects being removed, I lay a horse-shoe magnet on the table before me, with its poles turned directly from me, the northward limb being on my left hand, the southward limb-pole on my right, and experiments parallel to those just described are made, the results remain the same. If, near one side of the horse-shoe magnet, I lay my left hand on the table, the palm downwards, the thumb held wide of the fingers, the ring, if suspended half an inch from and above either of the finger-points, displays clock-rotation; suspended similarly before and above the point of the thumb, versed-rotation. Or the fingers of the left hand, so disposed, may be compared, in reference to Od, to the northward pole of a horse-shoe magnet, while the thumb corresponds with its southward pole.
If, removing my left hand, I turn the horse-shoe magnet, without altering the side on which it rests, half round, so that the poles point directly towards me, the northward pole being now, of course, on my right, the southward pole on my left, the ring held as before over either of the two poles, displays the same results. If I now move the magnet still nearer to me, so that its two poles are an inch beyond the edge of the table, I can obtain results which furnish a more precise explanation of the two rotatory movements already described, than I had before arrived at.
If I now suspend the ring, with its lowest part on a level with the magnet, and half an inch from its northward pole—that is, half an inch nearer me—it begins to oscillate longitudinally, with a bias towards me, as if it were repelled from the pole of the magnet. If I then suspend the ring an inch vertically above the first point of suspension, it begins to oscillate transversely, with a bias towards the right, or as if impelled by a dextrad current. If I then lower the ring half an inch, the first effect observed is, that it oscillates obliquely, being evidently impelled at once to the right and towards me—that is, in the diagonal of the two forces, of each of which I had before obtained the separate influence. In this third variation of the experiments, I have brought the ring to the limit of the two currents, where both tell upon it. This oblique oscillation soon, however, undergoes a change: it changes into clock-rotation, showing that the transverse or dextrad current is stronger than the longitudinal or proximad current.
If parallel experiments be made at levels below that of the pole of the magnet, corresponding but opposite results ensue. If the whole series be repeated upon the south pole of the magnet, opposite but perfectly corresponding results are again obtained: and similar results may be obtained with the two poles of an egg.
II. The mode in which I have latterly educed the rotatory movements depending upon galvanism, has been this. I have laid two discs, one of zinc, the other of copper, one on the other, having previously moistened their surfaces with salt and water. Then, as I mentioned, the ring held over the middle of the zinc disc (that being uppermost) exhibits clock-rotation. Held over the middle of the copper disc, when that is laid uppermost, versed-rotation. I mentioned, too, that if held beyond, but near the circumference of the same discs, the direction of the motion of the ring is reversed.
The discs which I employ are circular, an inch and a half in diameter, and about as thick as a sovereign. Upon these I do not fail to obtain, when dried and used singly, the first series of phenomena described in the preceding letter. But it occurred to me to try what would be the result of suspending the ring over the two together, and alternately laid uppermost, when they had been well cleaned and dried. This is evidently a still simpler voltaic arrangement than when the salt and water is additionally used. The result was in the highest degree interesting. When I suspend the ring half an inch above the centre of the copper disc, (that being laid uppermost,) the first motion observed is transverse; but after a few oscillations it becomes oblique—dextrad and proximad combined, in the diagonal between the primary influences of the zinc and of the copper. This change does not last long; the transverse force again carries it, in this instance, and clock-rotation is permanently established. When the zinc is uppermost, the corresponding opposite phenomena manifest themselves; and in either case a reversed movement occurs, if the ring is held extra-marginally to the discs.
III. I may say that I have now obtained positive evidence that these motions of the odometer do not depend upon my own will, or the sympathy of my will with existing conceptions in my mind; for they succeed nearly equally well when the discs are covered with half a sheet of writing-paper. In nine cases out of ten, when I thus manage to be in perfect ignorance which disc, or what combination of the two, is submitted to the odometer, the right results manifest themselves, and the cause of the occasional failures is generally obvious. Let me add upon this topic, that one day, the weather being cold and wet, and myself suffering severely with rheumatism, the odometer would not move at all in my hand. On another day, late in the evening it was, when I happened to be much fatigued and exhausted, the ring moved, indeed, but every motion was exactly reversed; thus my left hand I found now obtained exactly the results which, on other occasions, I got with the right.
IV. But by what cause, then—through what mechanism, so to speak, are the movements of the odometer immediately produced? Early in the inquiry I made this experiment. Instead of winding the free end of the silk round my finger, I wound it round a cedar-pencil, and laid the latter upon the backs of two books, which were made to stand on their edges, four inches apart, with the Od-subject on the table between them, the ring being suspended half an inch above it. The ring, of course, remained stationary. Then I took hold of the pencil with my finger and thumb, at the point where the silk was wound round it; my finger and thumb rested on the silk; but no motion of the odometer ensued. Hence it follows, that the odometer is, after all, always set in motion by the play of my own muscles. I venture then to suppose that my sentient nerves, unknown to me, detect on these occasions certain relations of matter—let me call them currents of force—which determine in me reflexly certain sympathetic motions of the very lightest, and even of an unconscious character. This idea, which I am sure affords the just solution of the matter, is highly consistent with some observations which I have before recounted. It explains how the primary delicate impression should yield to the coarser influence of a strong conception in the mind, that this or that other motion of the ring is about to follow, or even to that of a vivid and, so to say, abstract conception of another motion. It explains what I have several times verified, that on certain days a person standing behind me with his hand on my ear, or on my shoulder, can, by an effort of his will (mine not resisting,) make the odometer which I am holding move whichever way he happens strongly to image to himself, without communicating the same to me. It explains to me on what the difference consists between those who can set the divining-ring in motion, without a conscious effort, and those who cannot. The former, it will be found, are persons of so great nervous mobility, that any such motions, if their occurrence be forcibly anticipated by them, will certainly be realized by their sympathetic frames. Among this class should be sought, and would still remain to be detected by experiment, those whose impressionability by Od should prove commensurate with their nervous mobility. Finally, I cannot doubt that the view which I have thus arrived at respecting the mechanism of the motions of the odometer, is equally applicable to the explanation of those of the divining-rod. I see that, through its means, many before anomalous facts, with the narrative of which I have not bored the reader, which emerged in my former trials of the divining rod, made by the hands of others, lose their obscurity and contradictoriness, and leave the whole subject in the condition of an intelligible and luminous conception.
N. B.—It is a pity that of the inquirers who now amuse themselves with investigating these subjects, very few realize in their minds the idea of Von Reichenbach, that Od, though often exhibiting the same relations with electricity and magnetism, is yet an utterly different principle.