IN recent experimental investigations of the lubrication at heavily stressed contacts, particular attention has been paid to measurements of the thickness of the lubricant film which, between gear teeth, is typically about 1µ. Using steel cylinders nominally in line or point contact the thickness of the film has been deduced from measurements of electrical capacity1,2 or from determination of the penetration through the gap of a well-collimated and carefully aligned beam of X-rays3. The purpose of this communication is to direct attention to the advantages of direct observation of the contact using transparent specimens when the thickness of the lubricant film can be deduced from the examination of white light fringes; these techniques are illustrated by a description of some preliminary observations of a point contact between crossed cylinders2 of ‘Perspex’.