On a static method of comparing the densities of gases

Abstract

The measurement of small differences of pressure to a fairly high degree of accuracy is not difficult. I have indicated a construction of a micromanometer which in its ordinary commercial form has a range of 3 or 4 cm. of height of a liquid column and reads to 0·005 mm. direct. Dr. Stanton describes a manometer constructed on Professor Chattock’s principle, having a reading sensitiveness of 0·0015 mm. of water, but the range is not stated. Lord Bayleigh, observing the contact between mercury surfaces and sharp points, obtained a sensitiveness of 0·0005 mm. of mercury with a range of about 1·5 mm. The idea of employing the micro-manometer for the determination of the relative densities of gases first occurred to me in 1901 in considering the corrections to a set of Pitot tube observations taken in a gas pipe situated some 20 feet above the manometer, and though a rough trial was carried out at the time it is only recently that I have had an opportunity of making an adequate test of the method.