Notices respecting New Books. 445 



but that they should likewise embrace a consideration of the 

 simultaneous variations in the mean daily values of the ele- 

 ments at various stations. We must, in fine, consider the 

 possibility at least of there being in the upper atmospheric 

 regions, not merely currents which present a solar-diurnal 

 variation, but others that have no such variation, while yet 

 they may be highly susceptible to changes in the Sun. The 

 double method of treating mathematically not merely the 

 solar-diurnal variation, but likewise the simultaneous changes 

 in the mean daily values of the elements, would thus appear to be 

 necessary, and sufficient for giving us the required informa- 

 tion. Already the Greenwich scheme of publication embraces 

 not merely information connected with the solar-diurnal 

 variation, but gives us likewise the mean daily values of the 

 three elements ; and if a complete system of this nature be 

 pursued by a sufficient number of well-equipped magnetical 

 observatories, we may hope soon to obtain reasonably complete 

 information regarding the existence and distribution of 

 currents in the upper regions of the Earth's atmosphere. 



LX. Notices respecting New Books. 



On the Sensations of Tone as a Physiological Basis for the Theory of 

 Music. By H. L. E. Helmholtz, M.D., 6fc. Second English 

 Edition. Translated with additions by A. J. Ellis, F.M.S., Sfc, 

 <$fc. Longmans, Green, & Go. : 1885. 



TT is now nearly a quarter of a century since the first appearance 

 -*- of this book, the most recent English edition of which lies before 

 us. It ought to be possible by this time to form a fairly grounded 

 judgment as to the permanent position the work is likely to occupy 

 in the discussion of the matters of which it treats. And the 

 verdict must, as it seems, be, that while errors have been committed 

 on a certain number of points, and there are deficiencies here and 

 there in detail such as must be inevitable in a work of such mag- 

 nitude, yet the great bulk of the book holds its own to a most 

 surprising extent, and bears minute investigation in a manner 

 characteristic of the work of a master hand. Within the limits of 

 a notice it would be impossible to attempt to convey an analysis of 

 the work, and I will only endeavour to emphasize a few points of 

 present importance. 



The first great controverted point is that dealt with at pp. 125-6. 

 This purports to be an experimental proof of the law that " the 

 quality of the musical portion of a compound tone depends solely 

 on the number and relative strength of its partial simple tones, 

 and in no respect on their differences of phase." Now I do not 

 think that the experiments described in support of this law are 

 sufficient, if opposed by other experiments, in which apparent 



