Recoil curves as shown by the hot-wire microphone

The subject matter of this paper deals largely with a description of a process which, in its bearing, appertains to physics rather than physiology, but as the application is entirely physiological, it has been decided to submit it as a physiological contribution. In 1916, one of us (W. S. T.), while at work on the perfection of the hot-wire microphone, which he had invented for the location of enemy guns, realised the possibilities of the hot-wire microphone for obtaining records of the pulse, apex beat, etc., and had actually taken records both from the wrist and neck, and had shown these to members of the medical profession.