Liquid Surface Interferometry

THE property that liquid surfaces have of indicating level is frequently employed in physical and engineering metrology. Surprisingly little use is made of the property of flatness which, with certain reservations, is possessed by a reasonably extensive liquid surface, which provides a naturally reproducible reference basis. The earth's radius of curvature causes the centre of a liquid surface of 25 cm. diameter to project by only 12 A. above the true plane intersecting its perimeter, if the effect of capillary curvature at the boundary region is omitted from consideration.