Contact of Smooth Surfaces

Abstract

THE experiments described in our paper have shown that small polished plates, whether clean or contaminated by vapours or liquids, approach within about 0.3 microns when brought gently together in a dust-free atmosphere. Clean plates showed the same separation in vacuo, and this distance corresponded with the known limit of flatness of the plates. Later experiments with polished glass plates up to 10 cm. in diameter have confirmed this conclusion, since, when placed together gently in the air of the laboratory, they frequently showed first order interference colours and a mean separation of about 0.3 microns. The exact separation under these conditions depended on the amount of dust present in the atmosphere, but it was seldom as great as 4 microns. There was no evidence for ‘floating’ either with clean or contaminated surfaces.