April i , 1909] 



NA TURE 



more from the point of view of a teacher, and, in 

 its early chapters, the theory of the internal-combus- 

 tion engine is developed on the assumption of a con- 

 stant specific heat. Later the variation of the specific 

 heat with temperature is discussed in general terms, 

 and the results of Clerk, Mallard, and Le Chatelier 

 are given. 



The principal feature of the work, however, is the 

 very full account of the growth and development of 

 the internal-combustion engine in America. 



All the well-known types are described and gener- 

 ally very fully illustrated. In this respect the work 

 is somewhat encyclopsedic in character, and ought 

 rather to be regarded as a reference book than a 

 text-book. The same remark applies to other sections 

 devoted to fuels, testing of engines, methods of regu- 

 lation, gas-engine auxiliaries, and the like. In all 

 these we find a mass of information, with copious 

 references to the original sources. 



Anyone wishing to obtain a good general idea of 

 present-day practice in .America will find this book a 

 valuable work. E. G. Coker. 



OVR BOOK SHELF. 

 AhhandJiiiigen ziir Physiologic der Gesichtsempfind' 



iiiigiu aiis deni physiologischen Insfitut zu 



Frcibiirg-i-B. Herausgegeben von J. von Kries. 



Drittes Heft. Pp. 192. (Leipzig: Verlag von 



J. A. Barth, 1908.) Price 6 marks. 

 This volume comprises the third series of collected 

 papers from the laboratory of Prof, von Kries at 

 Freiburg. The communications have all been pre- 

 viously published in the Zcilschrift fiir Psychologie 

 imd Physiologic der Si)!nesorga)iL', the earliest having 

 appeared in 1903. It is doubtful whether their re- 

 publication in this form will lead to recognition by a 

 larger audience, not because of any lack of inherent 

 excellence, but rather because of their highly special- 

 ised nature. 



The first paper is an interesting note on the percep- 

 tion of flicker in normal and totally colour-blind 

 persons. The researches of Schaternikoff tend to 

 show that the retinal rods possess a lower sensitivity 

 for rapid periodic variation in the intensity of the 

 incident light than the cones; hence more rapid rota- 

 tion of the disc in the usual method of eliciting the 

 flicker phenomenon is necessary to produce complete 

 fusion with the eye adapted for light than with the 

 dark adapted eye. It became of interest, therefore, 

 to investigate the behaviour of the totally colour-blind 

 eye in these circumstances. -At the suggestion of 

 Prof, von Kries, who had not a suitable case under 

 his-" observation, Prof. L'hthof'f carried out some in- 

 vestigations. He found that much more rapid rota- 

 tion — about three times — was necessary with the 

 normal eye to eliminate flicker than with the totally 

 colour-blind eye. 



Porter has investigated the relationship between the 

 intensity of illumination and the frequency of change 

 necessary to eliminate flicker. He found that the 

 curves representing this relationship show two parts, 

 each nearly straight, but having two different con- 

 stants. These curves are analogous to those obtained 

 by Konig for the relationship between visual acuity 

 and intensity of illumination. In the one case the 

 fusion frequency, in the other the visual acuity, is 

 proportional to the logarithm of the illumination. 

 Both, therefore, behave in identical fashion : with the 

 smallest intensities of light both increase slowly ; at 



NO. 2057, ^'OL. 80] 



approximately the same intensity a much more rapid 

 increase suddenly becomes apparent. The simplest 

 explanation of these phenomena is that there are two 

 mechanisms at work, one of which is influenced by 

 light of low, the other by light of higher, intensity. 



In succeeding papers Dr. Wilhelm Trendelenburg 

 records quantitative estimates of the bleaching of 

 visual purple by monochromatic light and (with Dr. 

 Roswell P. .Angler) of mixtures of complementary 

 colours to form white. Siebeck has investigated the 

 intensity of monochromatic light in extremely small 

 fields, so small, in fact, as to eliminate the colour 

 element (Minimalfeldhelligkeit). Prof, von Kries, in 

 a paper founded on observations by Dr. Eyster, calcu- 

 lates in absolute terms the energy necessary for 

 stimulation of the retina, and Dr. F. P. Boswell 

 applies the same principles to the fovea. They thus 

 attempt what has already been done for the ear by 

 Lord Rayleigh and others. Other papers on colour 

 mixtures and colour memory will repay perusal, and 

 Prof, von Kries describes a simple apparatus for the 

 mixture of monochromatic lights which may be com- 

 mended to the notice of teachers of physiological 

 psychology. 



Fresh-water Algae from Burma, including a few 



from Bengal and Madras. By W. West and G. S. 



West. Pp. 175-260; 7 plates. (.Annals of the 

 Royal Botanic Garden, Calcutta, vol. vi., part ii.) 



Price Rs. 10, or 155. 

 The material was collected in certain districts of 

 Burma, and a few species in the Burdwan district of 

 Bengal and Vizagapatam district of Madras by Mr. 

 I. H. Burkill, and was forwarded for determination 

 by Lieut. -Col. Prain, at that time director of the 

 Botanical Survey of India. The work is almost 

 entirely systematic, as would be expected in dealing 

 with material from districts where the algal flora was 

 previously almost unknown, and has added very 

 materially to our knowledge of the distribution of 

 fresh-water algae in the Indian region. Two new genera 

 are described — Euastridium, a large and handsome 

 Desmid. possessing peculiar morphological features, 

 and Burkillia, belonging to the Protococcacefe, occur- 

 ring as free-floating colonies furnished with stout 

 horns. .Among the many new species described, 

 Mougeotia producta is of special importance because 

 of the presence of aplanospores in no way different 

 from those which are found in the genus Gonatonema. 

 In the last-named genus aplanospores only are formed, 

 whereas in Mougeotia, aplanospores and spores, as 

 a result of conjugation, are both present, hence it 

 may be necessary to place Gonatonema merely as a 

 section of the genus Mougeotia, in which spores re- 

 sulting from conjugation have ceased to exist. Uro- 

 coccus tropicus is remarkable in being green, vi'hereas 

 the cells of other species of the genus usually con- 

 tain an abundance of a red-brown pigment. 



The collection contained a number of interesting 

 Desniids which, with previous records, are said to 

 furnish material for a very interesting discussion on 

 their distribution in the East Indies generally. Even 

 from the knowledge forthcoming, certain Desmids 

 appear to be confined to an area extending from India 

 and Ceylon, across Burma and the Malay Peninsula 

 to Sumatra and Java, and thence to Queensland. 



As evidence of the wide geographical range of some 

 species of algae, Xostoc liiimiftisum, first recorded 

 from Scotland, and Plcctoncma '^vollei, from the 

 United States, were included in the collection. 



The number of varieties and forms hovering around 

 many of the species suggests that, from the stand- 

 point of de Vries, many incipient species are being' 

 produced. 



