Alan Walsh was the originator and developer of the atomic absorption method of chemical analysis, which revolutionised quantitative analysis in the 1950s and 1960s. Atomic absorption provided a quick, easy, accurate and highly sensitive method of determining the concentrations of more than sixty-five of the elements, rendering traditional wet-chemical methods obsolete. The method has found important application world-wide in areas as diverse as medicine, agriculture, mineral exploration, metallurgy, food analysis, biochemistry and environmental control, and has been described as 'the most significant advance in chemical analysis in the twentieth century'.