Thomson, James (1822–1892)

Irish physicist and engineer who in 1849 discovered that the melting point of ice decreases with pressure. He was also an authority on hydrodynamics and invented the vortex waterwheel in 1850.

Thomson was born in Belfast, the elder brother of the future physicist William Thomson, Lord Kelvin. He was only 12 when he began to attend Glasgow University with his younger brother, obtaining his MA in 1839. He held a succession of engineering posts before settling in Belfast in 1851 as a civil engineer. He was professor of civil engineering at Belfast 1857–73 and at Glasgow 1873–89.

The vortex water wheel was a smaller and more efficient turbine than previous designs, and it came into wide use. Thomson continued his investigations into whirling fluids, making improvements to pumps, fans, and turbines.

Thomson's discovery about the melting point of ice led him to an understanding of the way in which glaciers flow. He also carried out detailed studies of the phase relationships of solids, liquids, and gases, and was involved in both geology and meteorology, producing scientific papers on currents and winds.