Sillometer

It is moved by a paddle, that may be placed under the keel at will, and is supported by a plug sliding in a tube like that of the sillometer, but turning with the paddle and the rod.

The sillometer has a dial upon deck which constantly shews the number of miles per hour that the vessel is going; consequently it is easy to discover, under all circumstances, what is the best trim of the vessel, and the most advantageous quantity and distribution of the sail for obtaining the greatest speed. As the sillometer shows immediately the effect which every alteration in the sails or trim of the ship has on its velocity, it follows also that ships fitted with the sillometer can constantly maintain the speed they may have agreed upon, and so keep company together, and maintain the same relative position, though, from the darkness of the night or thickness of the weather, they cannot see each other

Moved sundry weights aft, viz., boat, brass guns, anchors, oars, &c. : for an instant the speed, as shown by the sillometer, diminished to 7-4 miles per hour, but it almost immediately increased to the former speed of 8 miles per hour. Moved the same weights forward, but could not perceive any sensible difference in the speed of the vessel. The speed, as shown by the sillometer, varied from 8.1 to 8.2 miles per hour. Tried the speed of the vessel by the common log, which gave 8 1/4 miles. The sillometer indicated exactly the same.

Satisfactory experiments have been made on board the Lightning steam-vessel, with Mr. Clement's Sillometer, and Marine and Steam Thermometers. The experiments commenced a short distance below Gravesend, and after a run of about 2 1/2 hours, Massey's log, with which the sillometer was compared, showed the distance run to be 15 1-10 miles -- the sillometer exactly 15 miles. An experiment was made by altering the course of the vessel several miles, and the sillometer indicated that during the operation the speed had decreased from 8 to 7 miles per hour.