Mechanical

Of course there is in a case like that just considered no question of a mechanical disturbance of the system under investigation during the last critical stage of the measuring procedure. (Niels Bohr)

Indeed I have very little idea what this means. I do not understand in what sense the word ‘mechanical’ is used, in characterizing the disturbances which Bohr does not contemplate, as distinct from those which he does. (John Bell)