Jones uses in his theory a two-parameter diagram to visualize how vowels are produced and he promoted the term cardinal vowel. The two parameters are tongue height and lip-shape. Many later models at the end of the twentieth century are still based on this model.
Jones studied the phonetics of various languages. In particular for example he did an analysis of the tone in Tswana. He developed new alphabets for African and Indian languages.
Source: R. E. Asher, The encyclopedia of language and linguistics, Pergamon Press, 1994