began studying the distribution of marine animals in space (depth range) and time (seasonality). His first research was with Edward Forbes conducting dredging in the Irish Sea. Other participants were Robert MacAndrew, John Gwyn Jeffreys, the Yoxford, Suffolk shell collector George Barlee (1794-1861) and his fellow Irishmen Robert Ball, Edmund Getty and George Crawford Hyndman. In 1835 he travelled in France, Switzerland and Germany with Forbes. Then in 1841 he joined Forbes and Thomas Abel Brimage Spratt on the Beacon commanded by Thomas Graves and working in the Mediterranean and Aegean. The expedition lasted eighteen months and conducted more than one hundred dredging operations at depths varying from 1 to 130 fathoms, as well as shore-based studies. Thompson focused on the depth range of algae, his main collection of which is in the Ulster Museum herbarium and consists of five large albums containing specimens collected by Thompson himself, William Henry Harvey, Moon, D. Landsborough, Robert Ball, Thomas Coulter, George Crawford Hyndman, William McCalla and many others. His records are also reported by others such as Gifford (1853):- Griffithsia simplicifilum from "...Isle of Wight, in August, 1841, by Messers. R.Ball. and W. Thompson." George Dickie's Flora of Ulster contains records of Thompson's frequent botanical contributions and his Hortus Siccus and he is mentioned in William Baird's Natural History of British Entomostraca. Later years Thompson corresponded extensively on all aspects of natural history with naturalists in both Britain and Ireland, including with zoologist Thomas Bell who was at the heart of the English scientific establishment and two of the "Grandees" of the Zoological Society, Nicholas Aylward Vigors, William Ogilby. As Thompson's reputation spread, information was passed to him by interested observers all over Ireland. However his health became poor around 1847 or 1848, when he was 42, and he suffered from heart trouble from 1847. In 1852 Thompson died of a heart attack in London where he had been tended by his friends William Yarrell, author of British Birds, Edward Forbes, Edwin Lankester, of the Ray Society and George Busk. He died unmarried. Excerpts from Thompson's letters and his notes were edited and published as the fourth volume of The Natural History of Ireland, which focused on invertebrates and non-avian vertebrates, by George Dickie, James Ramsey Garrett and Robert Patterson in 1856, four years after his death. Works Partial list from over eighty. A complete list is found in The Natural History