Antique depth sounding machine by Edward Massey.

Mechanical sounding machines replaced the traditional sounding lead and were used to determine the depth of water beneath a ship. This early 19th-century Edward Massey model is made of brass and has a rotor which drives a pair of counters, one on each side of the instrument. When in use it is attached to a rope and lowered through the water, as it descends the rotor turns and transfers the revolutions onto the dials. Once the device reaches the seabed the rotor is automatically locked and it can be pulled back up to the surface, the maximum depth is recorded on the dials. The dial on the front is marked zero to ten fathoms and the dial on the reverse side is marked zero to 150 fathoms. The mechanical sounding machine was patented by Edward Massey in1802.

Edward Massey was a leading London nautical instrument maker and he invented and perfected several nautical instruments. He received the first patent for a successful mechanical log - British patent 2601 in March 1802. The British Board of Longitude awarded Massey £200 for his invention and they recommended that the British Royal Navy purchase five hundred units for their fleet of vessels. Massey’s mechanical logs quickly became a commercial success and many ships used his "patent logs" throughout the nineteenth century.