October 26, 1905] 



NA TURE 



627 



changed its course as the Yellow River has? What 

 other country in the world has built a Great Wall ? 

 We are accustomed to hear much of the peculation 

 of the officials, but Mr. Little does not emphasise 

 this; in many districts the officials are revered and 

 beloved by the people. 



Consider the Yangtse Valley, again, where ocean 

 steamers can reach Hankow, where steamers with Mr. 

 Little himself as their pioneer have reached to Chung 

 King, and lately still further. This magnificent river 

 will undoubtedly remain the great high road for ccm- 

 nierce into Central China ; but railways are and will 

 be built to act as feeders to the main line, much to the 

 profit of the shareholders and of the inhabitants, for 

 Chinese are born traders, and already make use of 

 the pioneer of Chinese railways — the line from 

 Tientsin to Peking^in large numbers. 



Finally, we have a vivid description of the southern 

 basin, Canton, Hong Kong, and the provinces 

 bordering on French territory. Yunnan, which 

 adjoins our Burma, has a particular interest to 

 Englishmen ; but here, owing to our supineness in 

 days gone by, we have allowed the French to get 

 ahead of us with their railway, which will un- 

 doubtedly draw to itself all that is valuable of the 

 trade of the province. 



There was a time when many people thought that 

 China would be divided among the Great Powers — 

 that notion is exploded ; then came that of spheres of 

 influence — but we have seen this idea also put aside ; 

 the policy of the " open door " is all that remains. 



We congratulate Mr. Little on having given us a 

 most readable volume, full of information, and yet 

 with that local colouring which is an essential for a 

 book to command the attention of the general reading 

 public. 



ABSORPTION SPECTRA. 

 Haiidbiicli dcr Spectroscopic. By Prof. H. Kavscr. 

 \'ol. iii. Pp. viii + 604. (Leipzig: S. Hirzel, 1905.) 

 "VTJHF.N Prof. Kayser published the first volume 

 V V of his " Handbuch der Spectroscopic," he said 

 that the third volume would be devoted to absorption 

 spectra and cognate phenomena. He has, however, 

 found it necessary to treat the subject in two volumes, 

 the first of which contains the methods of investi- 

 gation of absorption spectra, the variability of absorp- 

 tion, the connection between absorption and chemical 

 constitution, and, finally, a list of all the measure- 

 ments of the absorption spectra of inorganic and 

 artificial organic substances. In the next volume the 

 absorption of the natural colouring matters in the 

 animal and vegetable kingdom will be described, 

 together with the relation of dispersion and fluores- 

 cence to absorption and, lastly, phosphorescence. 

 The present volume is peculiarly interesting, as it 

 deals to a great extent with the application of spectro- 

 scopv to chemical and physicochemical problems. 



In the first chapter Prof. Kayser deals with the 



apparatus and methods of investigation of absorption, 



and includes a discussion upon the nature and laws 



of absorption. It is well known that considerable 



NO. 1878, VOL. 72] 



confusion exists with regard to the terms used by 

 various experimenters, as, for example, absorption- 

 coefficient, &c. Not the least important section of this 

 chapter is that in which the author discusses these 

 and proposes a uniform set of definitions upon a 

 proper physical basis. In the discussion of the nature 

 of absorption. Prof. Kayser is perhaps a little obscure. 

 He very properly divides absorption into two kinds, 

 namely, the ordinary kind for which Kirchhoff's law 

 holds, and the so-called metallic reflection for which 

 the law does not hold. On p. 9 Prof. Kayser says, in 

 referring to those bodies which show surface colour. 

 I.e. metallic reflection, that these bodies show well 

 marked absorption bands, and that the particular rays 

 are wanting in the transmitted light, not so much 

 because they are strongly absorbed, but because they 

 are strongly reflected. This statement is rather mis- 

 leading. The phenomenon of metallic reflection is 

 shown by two classes of bodies, firstly, the metals 

 which are perfect conductors, and, secondly, those 

 substances which show surface colour and are not 

 conductors, as, for example, the aniline dyes. Prof. 

 Kayser's remarks, strictly speaking, only apply to 

 the first group, i.e. the metals, because as these 

 bodies are conductors the light cannot penetrate below 

 the surface. In the case of the substances belonging 

 to the second group the mechanism must be some- 

 what different. When a moderately dilute solution of 

 an aniline dye, such as rosaniline, is examined by 

 transmitted light, a very strong absorption band is 

 developed in the green. No surface colour is visible, 

 and undoubtedly the disappearance of the green rays 

 is due to the absorption of these rays by the molecules 

 of the dye. On the theory of resonance, the dye 

 molecules vibrate in sympathy with the green rays 

 and scatter the incident energy. If now the solution 

 is concentrated, the absorption on the surface becomes 

 greater, that is to say, the number of resonating 

 molecules in the surface is increased, until eventually 

 the scattering of the light becomes visible, and we 

 have the surface colour of the same wave-length as 

 the absorption band. It is not accurate to say that 

 the light is reflected rather than absorbed, because 

 in dilute solutions the rays penetrate to a considerable 

 distance before being absorbed. 



In the second chapter Prof. Kayser deals with the 

 variation in the absorption spectra of substances with 

 variation in the external conditions. Here he points 

 out that the extraordinary changes undergone by 

 absorbing substances with changes in the solvent, 

 dilution, &c. , show clearly what a mass of useless 

 work on absorption spectra has been published owing 

 to the observations having been made under very 

 limited conditions. The most interesting section of 

 this chapter is that in which the variations of the 

 absorption spectra of coloured metallic salts with 

 dilution change are discussed. A great many observ- 

 ations have been made by Ostwald and others upon 

 the absorption of coloured salts and the results pub- 

 lished in support of the ionic theory. Unfortunately, 

 more recent experiments have shown that the absorp- 

 tion by the different salts of the same metal and that 

 bv the different salts of the same acid show small 



