Gray and Joseph Dalton Hooker went to visit Richard Owen at London's Hunterian Museum in January 1839. Gray met Charles Darwin during lunch that day at Kew Gardens, apparently introduced by Hooker. Darwin found a kindred spirit in Gray, as they both had an empirical approach to science, and first wrote to him in April 1855. During 1855–1881 they exchanged about 300 letters. Darwin then wrote to Gray requesting information about the distribution of various species of American flowers, which Gray provided, and which was helpful for the development of Darwin's theory. This was the beginning of an extensive lifelong correspondence.