(_h_) The index in this instrument is secured upon the outer end of a pivot supporting a pulley of about ¾ of an inch in diameter. The spring consists of a coil of brass wire, of which one end is fastened into the inside of the roof-board (_c_) of which the outside forms the surface for the letters, &c., while the other end of the wire is prolonged beyond the coil to about 2½ inches, and, by means of a loop, has a string of catgut tied to it securely. This string is fastened to a perforation in the pivot. Another piece of the same kind of string is fastened to the circumference of the pulley. The pivot being turned so as to wind upon it the string proceeding from the spring, and thus constraining it so as to make it capable of effectual recoil from the pulley, the latter may, with a little care, be made, as the spring recoils, to wind about it another string duly attached to its circumference. The strings being thus wound, (one to the right, the other to the left,) when the string attached to the pulley is pulled from the outside of the box, it is unwound therefrom, and meanwhile winds that attached to the spring upon the pivot. The reaction of the spring, when left to itself, reverses this process, producing the opposite revolution in the pulley. The index attached to the pivot of course turns in one direction or the other, as the pivot is actuated by the drawing out or retraction of the string which proceeds from it. This, at the outer end, is tied to a ring, which prevents it from receding into the box. (_i_) It is surprising with what readiness a spirit, even when unused to the apparatus, will, by moving the lever, actuate the index, causing it to point to the letters, words, or figures distributed on the face of the disk, as above mentioned. (_j_) The apparatus of Pease above described, agreeably to the design of the maker, operates by means of a string extending from the brass ring, in which the pulley string terminates externally, to a weight situated upon the floor, so as to be taut when at rest. When this arrangement is made, tilting of the table, by raising the end at which the box is situated, causes the weight to pull the string, and of course to induce the revolution of the pulley, its pivot, and corresponding index. The restoration of the table to its usual position reverses the motion. Hence by these means the index may be moved either way, as requisite for the selection of the letters required for communicating.