398 Notices of Books. [July, 



the attainment of that higher beauty which appeals to the in- 

 tellect, harmony and disharmony are only means, although 

 essential and powerful means. In disharmony the auditory 

 nerves feel hurt by the beats of incompatible tones. It longs 

 for the pure efflux of the tones into harmony. It hastens towards 

 harmony for satisfaction and rest. Thus both harmony and 

 disharmony alternately urge and moderate the flow of tones, 

 while the mind sees in their immaterial motion an image of its 

 own perpetually streaming thoughts and moods." 



The fourth lecture treats of " Ice and Glaciers," and discusses 

 in some detail the various views of Tyndall and others in re- 

 gard to the formation of ice, the compression of snow into ice, 

 and regelation. 



In the next lecture, which was delivered in Konigsberg in 

 1854, the author discusses the " Interaction of Natural Forces." 

 In this we have an admirable account of the transmutation of the 

 various so-called physical forces, and of their relationship to 

 each other. The connection is clearly and cleverly traced, and 

 is illustrated very happily by examples. Some of us will re- 

 member that when in 1798 Rumford boiled water by friction, he 

 remarked that if fuel ever became scarce we could cook our food 

 by transforming mechanical action into heat, as he had then 

 done ; we did not, however, know before that " in some factories, 

 where a surplus of water power is at hand, this surplus is applied 

 to cause a strong iron plate to rotate rapidly upon another, so 

 that they become strongly heated by the friction. The heat so 

 obtained warms the room, and thus a stove without fuel is pro- 

 vided." In a town like Bristol, where the rise and fall of the 

 tide is considerable, the amount of heat which might thus be 

 obtained from mechanical sources would be considerable ; and if 

 water-mills to produce heat by friction were placed in the Rhone, 

 as it leaves the Lake of Geneva, all the poor of that city might 

 have their food cooked in a public kitchen, in which the heat 

 should be generated by purely mechanical means. 



The sixth lecture is entitled " The Recent Progress of the 

 Theory of Vision," and is translated by Dr. Pye-Smith, of Guy's 

 Hospital. The eye is discussed from a threefold point of view : 

 physical, physiological, and psychological; the latter treats of 

 the mental realisation of the changes which take place in the 

 optic nerve. In summarising the conclusions regarding the 

 perception of sight, the author remarks that "the correspondence 

 between the external world and the perceptions of sight rests, 

 either in whole or in part, upon the same foundation as all our 

 knowledge of the actual world — on experience, and on constant 

 verification of its accuracy by experiments which we perform 

 with every movement of our body. It follows, of course, that 

 we are only warranted in accepting the reality of this corres- 

 pondence so far as these means of verification extend, which is 

 really as far as for practical purposes we need." 



