Wilhelm Eduard Weber
After a further period of study in Germany with Wilhelm Eduard Weber and Hermann von Helmholtz, he returned to England, where his knowledge of spectrum analysis led to him being appointed to lead an expedition to Siam, to photograph the coronal spectrum during the total solar eclipse of 6 April 1875. This was an important appointment for such a junior scientist. On the way, he wrote a letter dated 21 February 1875, to "Nature" describing his observation of the "green flash" phenomenon.