Burt's Buoy and Knipper explained

You may have read this morning's book report and thought - what the hell is a Knipper? Thanks to diligent word-hound Michael Lean of Surrey Hills, Victoria we now know this is a Knipper. I don't know where the K went.

Figure 55. Burt's nipper, invented by Peter Burt, a British ship builder, in 1818. It was used to keep the sounding line vertical in spite of the motion of the ship. It was used by the British Admiralty along with a device of the same type designed by Massey. Credit: Sailing for Science - the NOAA Fleet Then and Now.