Notices respecting Neio Books. 391 



Recapitulation. 



(a) There is an interference in the perception of sound ; for 

 two simple tones capable of interfering are still heard to inter- 

 fere when conducted separately to the two ears. 



(b) When two simple tones in unison reach the ears in op- 

 posite phases, the sensation of the sound is localized at the 

 back of the head. 



(c) The localization of this acoustic " image" is independent 

 of the pitch of the sounds. 



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

 localized partly in the ears and partly at the back of the head, 



(e) Jf the difference of phase be complete but the intensities 

 unequal, the acoustic " image," instead of being at the middle 

 of the back of the head, is nearer that ear in which the sound 

 is louder. 



(/) It is possible to discern the difference between two 

 compound tones which differ only in the phase but not in the 

 pitch or intensity of their component partial tones. For when 

 two such compound tones are separately brought to the ears 

 so that the vibrations of any partial tone present reach the ears 

 in opposite phases, that particular partial tone is singled out 

 and localized at the back of the head, 



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

 differential tone is heard ; there is some evidence that summa- 

 tional tones are heard. 



(Ji) To binaural audition dissonances are excessively dis- 

 agreeable, and ordinary consonances harsh. 



{%) Vibrations mechanically conveyed to a point of the 

 parietal or occipital region of the skull, at one side, are appa- 

 rently heard in the ear of the other side of the head. 



University College, Bristol, 

 July 30, 1878. 



LI. Notices respecting New Boohs. 



A Treatise on Dynamics of a Particle, with numerous Examples. By 

 Peter Gutheie Tait, M.A., formerly Felloiv of St. Peter's College, 

 Cambridge, Professor of Natural Philosophy in the University of 

 Edinburgh, and the late William John Steele, B.A., Fellow of 

 St. Peter's College, Cambridge. Fourth Edition, carefully revised. 

 London : Macmillan and Co. 1878. (Crown 8vo, pp. 407.) 

 HPHIS work has been long before the world, and its merits as a 

 ■*■ comprehensive handbook of the subject are well known. In fact 

 it contains an account of the Motion of a particle under various cir- 

 cumstances amply sufficient for the requirements -of the most ad- 



