Improving one's touch

It is described here an effect which does not seem to have been reported previously, even though it must be familiar to certain craftsmen, and which is claimed that eminences no higher than 0.001 mm etched on to smooth glass can be detected.

Abstract

DRAWING the finger tips across a smooth surface usually induces sensations of pressure, warmth or cold, and roughness or smoothness. Any abrupt discontinuity is easily felt: it has been claimed that eminences no higher than 0.001 mm etched on to smooth glass can be detected, provided some movement of the finger tips is permitted1. We describe here an effect which does not seem to have been reported previously, even though we think that it must be familiar to certain craftsmen.