A Dictionary of Music and Musicians/Grasshopper
GRASSHOPPER or HOPPER, in a square or upright pianoforte of ordinary London make, is that part of the action known technically as the escapement lever or jack, so constructed with base mortised into the key and back piece, that it may be taken out or replaced with the key, without disturbing the rest of the mechanism. There is a regulating screw perforating the jack, tongue, or fly, as it is variously called, of the grasshopper, drilled into the backpiece and bearing a leather button, the position of which and the pressure of a spring determine the rake of the jack, and consequently the rise and rebound of the hammer; the rebound being further regulated by a contrivance attached to the jack, when not an independent member, and used for checking or arresting it after the blow. In grand pianofortes, and in upright ones with crank lever actions, the escapement apparatus is less easily detached from the action.
It is not recorded by whom the Grasshopper was introduced, although the escapement part of it existed in Cristofori's 'linguetta mobile'; but the tradition which attributes it to Longman and Broderip, pianoforte makers in London, and predecessors of the firm of Clementi and Collard, may be relied upon. John Geib patented in London in 1786 a square action with the jack, and the setting off button acting upon the key, also, in another form, the screw holding the button perforating the jack—but with the button in front of it. The improved form with which we are acquainted, with the button behind the jack, was adopted by Messrs. Longman and Broderip, and soon became general.