On 17 August, 26 August, 21 October, and 10 November 1852 Welsh made, for the Kew committee, four ascents from Vauxhall, with the assistance of Charles Green, in his balloon the Great (or Royal) Nassau. The purpose was to make meteorological observations, and a detailed description was published in "Philosophical Transactions" in 1853. In March and May 1854 he made for the committee an investigation on the "pumping" of marine barometers, an artefact of the rolling motion of ships. In 1855 Welsh went to the Exposition Universelle in Paris for the exhibit of magnetic and meteorological instruments used at Kew. In 1856 he began at Kew a series of monthly determinations of magnetic field intensity and magnetic dip with instruments provided by Edward Sabine. In the same year Welsh was directed to construct self-recording magnetic instruments on models devised originally by Ronalds and improved by himself.