 Foster was elected a Fellow of the Royal Society in 1869, serving two terms as its vice-president in 1891–3 and 1901–3.He was president of section A of the BAAS in 1877 and was general treasurer of the association from 1888 until 1904.In the course of his many investigations to measure and compare standards of electrical resistance Foster adapted the Wheatstone bridge to measure small differences (rather than ratios) of resistance.