Recoil Curves as shoivn by the Hot- Wire Microphone. 289 



in the neighbourhood of 82 - 3 gramme-metres per beat, of which 81"6 units 

 represent work done against arterial pressure, and 0*7 units are measured in 

 kinetic energy at the root of the aorta. The latter again is considerably 

 greater than the value obtained by our experiments, since our measurements 

 are integral of all movements footward and headward. 



One other point should be referred to before proceeding. Yandell 

 Henderson obtained records of displacement variation, and these in a given 

 mass, that of the patient with the platform that supports him, are also records' 

 of the potential energy of that mass. 



Thus it will be seen that the measurements made by Yandell Henderson 

 and ourselves are complementary, since in any vibrating system the total 

 energy at any time is the sum of its potential and kinetic energies. The two 

 quantities will be out of phase 7r/2, maximum potential energy correspond- 

 ing to minimum kinetic energy, and vice versa. 



The peaks of the displacement curve correspond to the minima of the 

 records of this paper. Also, while the displacement curves can indicate 

 positive and negative values, the curves of our records only give positive 

 values. Allowing now for the change of phase of 7r/2 on passing from one 

 •curve to the other, and remembering that the values of the kinetic energy 

 curves are always positive, it is possible to show a resemblance between the 

 two sets of curves. 



Fig. 4 is a reproduction of a diagram from Yandell Henderson's paper. 

 Taking fig. 3, B, to represent a characteristic heart record obtained by the 

 process described in this paper, the curve of fig.. 4 can be approximately 

 reproduced by reversing alternate peaks to allow for positive and negative 



Fig. 4. 



-effects. The change of phase would be imposed by moving the curves as a 

 whole through the width of half a peak, bearing in mind also that whereas 



