This trick, which dates back many, many years, has been revived within the last two or three years in a greatly improved form. When first exhibited, the motive power was electricity and the clock was a piece of fine but delicate mechanism, easily put out of order. After a while some clever fellow took hold of it and changed it so that it might be worked by a string, but the way in which the arrow, that serves the purpose of a hand, was connected with the string was decidedly awkward. In time, however, some other clever fellow remedied that by stretching the string across the frame from which the clock was suspended. In this way when hanging the clock in place, the string was caught over the little grooved wheel at the back of the dial, that keeps the arrow in place.
Even then the trick was restricted to the use of the conjurer who had his own stage to work on, for it needed an assistant back of the scenes to pull the string, and that was almost an insuperable objection on the vaudeville stage.
It remained for a third clever fellow an experienced performer, with a genius for mechanics, Mr. Frank Ducrot, to devise an entirely new way of working the trick, so as to dispense with an assistant.
The clock is simply a dial of clear glass or what is better of transparent celluloid. When made of the latter the numbers and the inner and outer ring are cast in one solid piece of brass, thus almost precluding the danger of breakage. In the center of the dial is fitted a brass piece with a hole to admit of a spindle. This spindle which is of steel, passes through the exact center, from the back to the face of the dial, and through a corresponding hole in the arrow which is thus attached. On the other end of this spindle is a small, deeply grooved wheel. Over this wheel is a strong, black thread. Before exhibiting the trick, the dial is prepared by being set in a frame, and one end of the thread is attached to a light spiral spring concealed in the upright of the frame. The other end of the thread after passing over the groove of the wheel is carried down through the upright, coming out at the foot. From there it is led to a table, at a little distance from the frame, and laid on it. A sharp, black hook is tied to this end of the thread. In its normal position the arrow points to twelve, but at a pull on the free end of the thread it will move to any desired hour, and will be brought back to twelve by the action of the spring which is nicely adjusted. But how can the thread be pulled without attracting the attention of the audience? The performer quietly picks up the little hook and sticks it into the leg of his trousers. He is now free to move away until the thread becomes taut. When that occurs a very slight movement of the leg or the least pressure of the body against the thread, will cause the arrow to revolve. It is absolutely under his control, and he can set it twirling round the dial if he wishes.
Sometimes a light weight is substituted for the spring. If desired, the clock may be hung from a cord that is attached to two chairs, or in other ways, according to the fancy of the performer. We are indebted to the courtesy of the inventor of this method of working the trick, Mr. Frank Ducrot, for this explanation, which has never been published till now.
Some performers use a loaded hand that may be set by means of a ratchet to point to any desired hour. This may be combined, with advantage, with the method first explained.