TRANSACTIONS OF SECTION D. DBPT. ANATOMY AND PHYSIOLOGY. 601 



MONDAY, AUGUST 19, 1878. 



The following Papers were read : — 



1. Phenomena of Binaural Audition.* 

 By Professor Silvanus P. Thompson, D.Sc, B.A. 



This paper resumed an investigation on which the author had read a paper in Sec- 

 tion A, the preceding year. The following points summarize the communication : 



(a) There is an interference of the perception of sound : for the tones of two 

 tuning-forks or other simple tones, differing slightly in pitch, and capable of inter- 

 fering, are still heard to .interfere when conducted separately to the two ears. 



(b) When two simple tones in unison reach the ears in opposite phases, the 

 sensation of sound is localised at the hack of the head instead of in the ears. This 

 and the preceding phenomenon are easily experimented upon with Graham Bell's 

 telephones, or with indiarubber tubes to bring the sounds to the ears. 



(c) This localisation of an objective acoustic " image " is independent of the 

 pitch of the sounds. 



(d) When the difference of phase is partial, the sensation is localised partly in 

 the ears, partly at the back of the head. 



(e) If the difference of phase be complete, and the intensities unequal, the 

 acoustic " image," instead of being at the middle of the back of the head, is nearer 

 to that ear in which the sound is louder. 



(f ) It is possible to discern the difference between two compound tones which 

 differ only in phase but not in pitch, or in intensity of their component partial tones ; 

 for when two such compound tones are brought to the ears so that the vibrations of 

 any partial tone present reach the ear in opposite phases, that particular partial tone 

 is singled out and localised at the back of the head. 



(g) When two simple tones are led singly to the two ears no differential tone is 

 heard. There is some evidence that summational tones are heard. 



(h) To binaural audition dissonances are excessively disagreeable, and ordinary 

 consonances harsh. 



(i) Vibrations mechanically conveyed to a point of the parietal or occipital 

 regions of the skull at one side of the median line are apparently heard in the ear 

 of the other side of the head. 



2. On the Theory -of Muscular Contraction. By G. F. Fitzgerald, M.A. 



Assuming a muscle to consist of fibriles averaging g^th of a centimetre in dia- 

 meter, and that they may be treated as a system of elongated cylinders of fluid 

 with a superficial tension capable of variation by the action of nervous stimuli in 

 accordance with M. Lippmann's experiments on the relations of electrical difference 

 of potential to the superficial tension of fluids, it may be shown that a force of 

 4 kilogrammes per square centimetre might be produced, which approximates to the 

 observed maximum contractile force. The striations in striated fibre are accounted 

 for by the instability of uniform fluid cylinders, the necessity for a continual 

 stimulus to keep up a given contraction by the constant repair going on in living 

 muscle, and the heating of a muscle when it contracts, is completely explained by 

 the fact that all fluid surfaces heat when they are allowed to contract under the 

 action of their superficial tension. 



3. On the Nervous System of Medusas. By G. J. Romanes, F.L.S. 

 * See ' Phil. Mag.,' Nov. 1878. 



