As early as 1807 the degree of LL.D. was conferred upon Brewster by Marischal College , Aberdeen ; in 1815 he was elected a Fellow of the Royal Society , and received the Copley Medal ; in 1818 he received the Rumford Medal of the society ; and in 1816 the French Institute awarded him one-half of the prize of three thousand francs for the two most important discoveries in physical science made in Europe during the two preceding years .