November 26, 19 14] 



NATURE 



333 



many cases a more artistic arrangement of the 

 material might have been achieved. Some pic- 

 tures, as that of the snowdrop, for instance, are 

 unworthy of the book. To the botanist the pic- 

 tures are of little value, owing to the absence 

 of an analysis of the parts of the flower and fruit, 

 and this defect is especially noticeable in the 

 case of the plates of the bulrush and Luzula, 

 which give no indication of the structure of the 

 flowers. It may be urged that such details are 

 relegated to special plates, but even then they 

 are so poorly executed and often on so small a 

 scale as to be of little assistance. It is un- 

 fortunate that the artist, who undoubtedly pos- 

 sesses considerable skill and has bestowed so 

 much labour on her drawings, had not sought the 

 best advice as to the way in which she might 

 have made her pictures of value. 



The notes supplied by Prof. Boulger are full of 

 useful information and make pleasant, if not very 

 strenuous, reading. We doubt, however, owing 

 to the bulk of the book, if they will receive very 

 serious attention. He has collected together a 

 good deal of curious and out-of-the-way informa- 

 tion under the different plants which it is well 

 to bring to the notice of students and those inter- 

 ested in flowers. In addition to the ancient lore 

 the correct naming of the plants is fully treated, 

 and a considerable amount of recent work of 

 interest is incorporated as occasion demands. 



Information about the habitats and general con- 

 dition of life of the different plants figured is also 

 given. In the introduction a useful outline of 

 general floral morphology and classification is 

 to be found, and the plates with their pages of 

 text follow. The plants figured in the volume in- 

 clude the British conifers, certain monocotyledons, 

 the willows, oak, beech, and allied trees, the 

 nettles, Polygt)naceae, Caryophyllaceae, and a few 

 others. 



PHYSICAL CHEMISTRY, 

 [j) The Theory of the Solid State. Based on 

 Four Lectures delivered at University College, 

 London, in March, 1913. By Prof. W. Nernst. 

 Pp. viii+ 104. (London : Hodder and Stoughton, 

 1914.) Price 25. 6d. net. 

 I2) Lehrbuch der physikalischen Chemie. By 

 Dr. K. Jellinek. Band i. Die Lehre von den 

 Aggregatzustanden, Teil 1. Pp. xxxvi + 732. 

 (Stuttgart : F. Ende, 1914.) Price 24 marks. 

 [3) Complex Ions in Aqueous Solutions. By Dr. 

 A. Jaques. Pp. vi + 151. (London: Long- 

 mans, Green and Co., 1914.) Price 45. 6d. net. 

 h) ' I ^HOSE who had the opportunity of hearing 

 J X Prof. Nernst deliver his short course 

 >f lectures at University, College, London, on the 

 NO. 2352, VOL. 94] 



Quantum Theory as applied to the solid state of 

 matter will welcome this somewhat belated publi- 

 cation. The book is a masterpiece of lucid con- 

 densation, covering as it does in a small number 

 of pages the whole range of modern work on the 

 thermal properties of solids. The limitations of 

 the Dulong-Petit generalisation are briefly dis- 

 cussed. The necessity for the introduction of 

 some new hypothesis in place of equipartition is 

 made clear, and the fortunate application of 

 Einstein of the Planck quantum concept to the 

 heat capacity of vibrating atoms is shown to point 

 the way to a new understanding of the baflfling 

 problem of the solid state. The Nernst-Linde- 

 mann empirical modification of the Einstein 

 formula is touched upon, and later the more 

 theoretically significant expression of Debye. 



Whilst fully realising the great progress which 

 has been made by the introduction of the quantum 

 theory to the thermal properties of solids (and 

 gases and liquids for that matter), it would be 

 idle to pretend that everything is at present on a 

 sure and certain basis. As a matter of fact 

 nearly every stage bristles with assumptions, and 

 although the general trend is certainly in the right 

 direction, not a few of the assumptions are 

 mutually conflicting. A science in this state is, 

 however, just at its most attractive stage, and the 

 number of investigations cited as references in the 

 book are ample evidence of the interest which the 

 subject has awakened, especially in Germany. 



An important feature of the book is the good 

 account of the experimental methods employed in 

 the Berlin laboratory for the determination of 

 specific heats, especially at very low temperatures. 

 Perhaps the most interesting section is that 

 entitled " General law respecting the behaviour of 

 solid bodies at very low temperatures," in which 

 a most suggestive account of present and future 

 problems is given on such subjects as thermal 

 expansion, compressibility, conduction of heat and 

 electricity, thermal e.m.f's, and magnetic sus- 

 ceptibility. It would seem that before long the 

 subject of thermal and electrical conductivity of 

 solids will be a region of controversy between the 

 electron view and the quantum view — which, it is 

 to be hoped, will result in a clearer physical con- 

 ception of what the quantum really is. It is note- 

 worthy that no mention is made of Sommerf eld's 

 views. 



There is no question that during the next 

 decade at least, the most active investigation in 

 theoretical physics and chemistry will consist in the 

 further extension and application of the quantum 

 theory, hence the significance of the present 

 publication which is a most excellent epitome 

 of the subject (so far as it refers to solids), by 



