The adherence of flat surfaces

Abstract

In recent years it has been found possible to polish plane surface of hardened steel to a degree of accuracy which had previously been approached only in the finest optical work, and to produce steel blocks in the form of end gauges which can be made to adhere or "wring" together in combinations. Considerable interest has been aroused by the fact that these blocks will often cling together with such tenacity that a far together with such tenacity that a far greater force must be employed to separate them than would be required if the adhesion were solely due to atmospheric pressure. It is proposed in this paper to examine the various causes which produce this adhesion: firstly, showing that by far the greater portion of the effect is due to the presence of a liquid film between the faces of the steel; and, secondly, endeavouring to account for the force which can be resisted by such a film. The only previous experiments in this direction appear to be those carried out with Whirworth surface plates by Prof. Tyndall in 1875. By wringing together two of these plates and suspending them in a vacuum he proved that the adherence between them was not caused solely by atmosphere pressure as had been previously supposed. According to Goodeve, the conclusion at which Tyndall arrived was that the plates adhered by the molecular attraction of the bearing points brought into close contact by reason of the near approach to absolute truth of surface. Frequent references have been made to these experiments, and the conclusion of Tyndall appear to have been generally accepted.