Perhaps I have presumed too much in heading this letter with the title of “The Solution.” But what is the solution of physical phenomena but the displaying of the forces which compel their sequence? As an inquiry progresses, a few general expressions take the place of the first imperfect and complicated explanation. But the first step made was still a solution; and the highest solution ever yet obtained has probably still to be merged in some expression yet more general. So the attraction of gravitation is probably connected with, or balanced by, a corresponding repulsive force, coming into operation at some enormous distance from the centre of each planetary sphere, and the two may eventually prove to form one law. But I had hoped that I was not presuming in asserting that the present inquiry has immediate practical applications, such as seldom fall to the lot of so young an investigation. The odometer may prove a useful test of the presence and qualities of electric, chemical, and magnetic actions; it will probably help to determine the electrochemical qualities of bodies; and in large or small crystalline masses—in the diamond, for instance—will serve to show the axes and distinguish the opposite poles. In reference to biology, it will probably furnish the long-wanted criterion between death and apparent death; for I observe that, with an egg long kept, but still alive, though no longer likely to be very palatable, the odometer freely moves in the way described in the fourth section. But it treats the freshest egg, when boiled, as if it were a lump of zinc. Nevertheless I am not without certain misgivings. I suspect that the divining-ring will be found to manifest genuine Od-motions in the hands of as small a number as succeed with the divining-rod. And I fear that overhasty confidence in results only seemingly sound, may lead many astray into a wide field of self-deception. 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.