Manometer to measure the flow of water
An improvement on Cole's pitometer was patented in 1908 by O.C. Smith and Paul Lanham, of Washington, D.C. They used an inverted U-tube so that they could use indicating liquids with lower specific gravity than water. They could then improve the pitometer's performance by selecting lower viscosity liquids for use in the manometer. Another improvement in their design was a water jacket around the manometer to prevent heating by the lamp used for exposure of the photosensitive chart paper.