This instrument is designed to measure the distance covered by a ship. The design consists of a hollow brass torpedo-shaped float bar which, after being attached to a rope, floats behind the ship. Below this is a brass register with four dials indicating the distance covered in nautical miles ('1/4-1', '1-10', '10-100') and feet ('10-100'). A brass rotor is connected to the register. This trails behind the device, connected to a rope, and spins in the water. The rotary motion is then passed through the register, driving the dials. This machine could also be used to measure the speed of the current in a river or stream. This form of speed log was patented by Edward Massey (about 1768-1852), whose name is inscribed on the converter, along with the trademark of three Ls in a triangle.
Fitted wooden glass fronted box.