Harding’s instrument was designed for dissecting organisms that were too large for existing micromanipulators but too small to be dissected using hand held tools. His instrument, which sat on the stage of a dissecting microscope, was based on the pantograph—a mechanical linkage, known since antiquity, that is used to precisely reduce a control input.
John Philip Harding (1911-1998), a zoologist at the British Museum (the part which is now the Natural History Museum), introduced this instrument in a paper read on November 16th, 1938. This included both a description of the mechanism as well as instructions for using it to prepare permanent slides containing the appendages of copepods (crustaceans typically 1-2mm long).
Because the instrument required two hands to operate, Harding devised an attachment for the focussing mechanism of a stereoscopic dissecting microscope so that that the operator could change focus with the knee.
Harding’s mechanism was built by Mr. H. J. McKay who was then a locksmith of the British Museum. I don’t yet know how widely it was used. [Harding 1939, 19-25]