SummaryAn investigation has been made of the effects of position and size of diaphragm ,apertures on the interference fringes in length interferometry. The results indicate that, while the well-known correction formula for the effect of the oblique rays from a point source off the optic axis is always applicable, the effect of finite area of aperture is a more complex one and is not in general proportional to the length measured. This effect depends essentially on the phase differences arising from different points of the aperture and is oscillatory in character. For a narrow slit the maximum fringe displacement arising from this effect is not greater than about 0·15 fringe. For a circular aperture the maximum effect is about O· 5 fringe and for a square aperture about o· 35 fringe.
An account is given of experimental studies of the nature of the strong adhesive contact between finely finished steel and glass surfaces when a trace of liquid exists between them. These surfaces are of the kind that are of practical use in length metrology where this adhesive action or ``wringing'' is of considerable importance.
The dimensional effects of the thin film between the surfaces have been measured by multiple-beam interferometry and the nature of the adhesive contact has been further studied by measuring tangential forces and electrical characteristics.
The experimental evidence suggests that there is no liquid film effectively separating the surfaces but that the strong adhesive action induced by the presence of the liquid introduces a dimensional contact error. This error is likely to be positive or negative, depending on the degree of contact between the surfaces. Provided the adhesion is good the contact error is not greater than ±0.01μ. Where such an error is undesirable in high precision length metrology it is better to avoid the use of this adhesive contact.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.