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without giving any indication of touching bottom and so its use was abandoned.
The Thomson machine consists of a reel or drum six feet in circumference, made of galvanized sheet iron. The drum is about four inches in width and has a rim on each side from one and a half inches to two inches in height. Around the right side of the drum runs a V groove which takes the endless rope or pulley line which controls the revolutions of the drum in sounding.
The drum weighs about 60 lbs., and will readily hold five miles of the piano wire. It rests on a light iron frame bolted to a wooden bed and can be readily unshipped when not required for use. Close behind the rim of the drum, and directly in line with the V groove, is fixed a light iron wheel ten inches in diameter; this wheel, called the dynamometer wheel, has one groove wide enough to hold two parts of line, and a second narrow groove to receive a cord simply. Back of this wheel is a common spring balance, which will register a strain of 110 lbs.
Some twenty-five feet from the reel is fixed a pully wheel, connected with the drum on one side, by the endless rope, and having a pendant on its other side running through a block suspended for the purpose. To the pendant are attached hooks from which to suspend weights of different sizes. The inventor used a tackle, instead of a pendant and weight, to be hauled taut as occasion required; but weights were substituted as being easier to manage and more satisfactory in their working, as by that means a steady, known and invariable strain could be had as desired, according as the weight of wire and sinker out, make increased power on the pulley necessary.
In getting the machine ready to sound, an endless rope of medium size is fitted into the grooves of the drum and pulley wheel, like an ordinary belt; then a full turn is taken round the dynamometer wheel, the latter being secured to the spring balance by a small cord resting in the narrow groove, and passing down through a small hole in the wheel; weights then being hooked to the pendant, the endless rope tautens, and the machine is ready for use.
