besides his mathematical works he wrote on theology, logic, english grammar and philosophy, and he was involved in devising a system for teaching a deaf boy to speak at littlecote house. william holder had earlier taught a deaf man, alexander popham, to speak "plainly and distinctly, and with a good and graceful tone". wallis later claimed credit for this, leading holder to accuse wallis of "rifling his neighbours, and adorning himself with their spoyls".