TRANSACTIONS OF SECTION A. 255 



currents traversing the second telephone set it swinging. In every case the differ- 

 ence of phase observed amounted to one quarter. 



In the case of those telephones which transmit vibrations by varying the resist- 

 ance of the circuit, instead of varying the electromotive force, there is no such 

 retardation of phase produced in the ordinary electromagnetic receiver. If, how- 

 ever, the current so transmitted is first passed through an induction coil, a re- 

 tardation of phase of one quarter is produced, and in the case of several successive 

 inductions the retardation amounts to an additional quarter for every additional 

 induction. This remark applies only to vibrations of harmonic and quasi-harmonic 

 type. Vowel sounds, which consist of compound harmonic vibrations, are un- 

 changed to the perception of the single ear, which is unable to distinguish differ- 

 ences of phase, or between compound sounds which differ from one another only 

 in the difference of phase of their components. The vibrations of consonantal 

 sounds, on the contrary, depart more and more widely from their original type at 

 each successive induction. 



In the case of Edison's niotographic or electro-chemical receiver, the velocities, 

 not the displacement of the disc, are proportional to the strength of the currents 

 received. Hence vibrations already retarded one quarter in transmission, as is the 

 case with those of the carbon transmitter in conjunction with its induction coil, 

 always used with this instrument, are restored to their primitive phase. The 

 vibrations of this receiver therefore agree in type, not with the vibrations of the 

 induction current (which correspond to the derived function of those of the original 

 vibration), but with those corresponding to the function of which the vibrations 

 of the induction current are the derivate ; that is to say, they agree in type with 

 the primitive vibrations of whatever form. Hence in the receiving telephone of 

 Edison consonantal sounds which depart widely from the purely harmonic type 

 are better rendered than in a telephone which like that of Bell both retards the 

 vibrations in phase and alters them in type. 





5. The Pseudophone. By Professor Silvanus P. Thompson, B.A., D.Sc. 



The pseudophone is an instrument whose object is to illustrate the laws of the 

 acoustic perception of space by the illusions it produces, just as the pseudoscope 

 of Wheatstone illustrates the laws of the optical perception of space by the ocular 

 illusions it produces. 



The pseudophone consists of certain adjustable reflectors which can be at- 

 tached to the head, and which perform the functions of the natural pinnae in 

 ordinary hearing. According to Steinhauser's theory of Binaural Hearing, the 

 acoustic perception of space depends upon the relative intensity with which a 

 sound-wave is received into the two ears, this again depending on the conforma- 

 tion and position of the head. Though in general true for many sounds, this 

 theory fails to account for certain observed facts in the perception of sound, and 

 fails in so far as it neglects differences of phase and of pitch. 



Experiments made with the pseudophone indicate the direction in which Stein- 

 hauser's theory requires modification. 



6. On the Tension of Vapours near Curved Surfaces of their Liquids. 



By G. F. Fitzgerald. 



The paper is intended to give a physical explanation of the fact that the tension 

 of a vapour in contact with the surface of its liquid when that surface is convex or 

 concave is greater or less respectively than when flat. It rests upon the assumption 

 that evaporation is not merely superficial, but that molecules are emitted from a 

 certain depth beneath the surface of a liquid. From this it follows that the 

 chances of escape of a molecule from a given depth below a convex surface are 

 greater, and from below a concave one less, than from a flat one. Taking the depth 



