526 



NATURE 



[January 22, 1920 



hemisphere in the opposite direction. It must 

 therefore be of supreme importance. 



Every serious student of meteorology should 

 obtain Part iv. of the manual and read it, and all 

 will hope that the other parts may be published 

 shortly. W. H. Dines. 



RESEARCHES ON FLUORESCENCE. 

 Researches in Physical Optics. Part ii. Reson- 

 ance Radiation and Resonance Spectra. By 

 Prof. R. W. Wood. (Publication No. 8 of the 

 Ernest Kempton 'Adams Fund for Physical Re- 

 search.) Pp. viii+ 184 + X plates. (New York : 

 Columbia University Press, 1919.) 



THIS is the second instalment of a valuable 

 re-publication of Prof. Wood's papers. The 

 first half of the volume deals with the spectroscopic 

 properties of iodine vapour, particularly the study 

 of the fluorescent spectrum with high resolving 

 power. The difficulty with this, as with most other 

 modern optical experimenting, is lack of light, and 

 the success attained in overcoming the obstacle by 

 well-thought-out optical arrangements is very re- 

 markable ; but the complexity of the phenomena 

 brought to light is such as may well make theo- 

 retical progress seem almost hopeless. 



It has been possible to obtain monochromatic 

 stimulation at one particular absorption line of the 

 iodine spectrum by the ingenious but simple device 

 of using the mercury vacuum arc as illuminant. If 

 the arc is run at low-current density, one line only 

 of the iodine spectnum is covered by the green 

 mercury line. Even in this case the result is to 

 stimulate not merely the line primarily excited, but 

 also a series of doublet lines, extending along the 

 spectrum on either side of the latter. Stokes's law 

 of fluorescence is thus completely violated. 



All this results from the stimulation of one line 

 only of the iodine spectrum. 



But this line is one of forty thousand, and it 

 appears that we can scarcely rely on it as being 

 typical, since the iodine lines are of many varieties, 

 as shown by their minute structure and by the 

 Zeeman effect and the magnetic rotatory proper- 

 ties. 



No doubt what is wanted for this class of re- 

 search is some means of obtaining intense mono- 

 chromatic stimulation of great purity, and with its 

 frequency under control over a wide range. Prof. 

 Wood is able to do something in this direction 

 by altering the current through the mercury arc, 

 and thereby the width of the green mercury line; 

 this makes it overlap several of the iodine lines, 

 and the complexity of the phenomena is thus 

 greatly increased. It is perhaps worthy of con- 

 sideration whether the Doppler effect obtained by 

 NO. 2621, VOL. 104] 



moving the source could be of service, but this 

 method would probably be very difficult of execu- 

 tion, and the range that could be hoped for very 

 far short of what is desired. 



The second half of the volume deals with other 

 phenomena of fluorescence in gases of a miscel- 

 laneous kind, but is marked throughout by the 

 same fertility of resource in devising experimental 

 methods. The re-emission of the mercury radia- 

 tion at wave-length 2536 when cold mercury 

 vapour is stimulated by this radiation is an ob- 

 servation of special importance ; the question 

 presses for answer how this resonance is related 

 by the scattering of white light by gases when 

 there is no resonance. R. 



SCIENTIFIC STUDY OF THE SUGAR 

 GROUP. 

 The Simple Carbohydrates and the Glucosides. 

 By Dr. E. Frankland Armstrong. Third edi- 

 tion. (Monographs on Biochemistry.) Pp. x-t- 

 239. (London : Longmans, Green, and Co., 

 igig.) Price 12s. net. 



THE third edition of Dr. E. F. Armstrong's 

 monograph is something more than a new 

 and revised issue ; it is, to all intents and pur- 

 poses, a new book. Such a statement may not, 

 on first inspection, seem to be well founded, as 

 the general scheme adopted by the author in the 

 earlier editions has been retained, and the sub- 

 division of the material into chapters remains 

 much as before. A comparative reading of the 

 texts, however, shows that some of the changes 

 introduced are fundamental, and a reader making 

 his first acquaintance with the specialised 

 chemistry of the carbohydrates through a study of 

 the latest edition will thus acquire not only much 

 new information, but also an entirely new per- 

 spective. 



The seven years which have elapsed since the 

 appearance of the second edition have been 

 marked by considerable activity in sugar research, 

 and the fact that Emil Fischer closed his career 

 by once more directing the work of his school to 

 this subject would almost in itself be sufficient 

 to make a fresh edition necessary. Many novel 

 and unexpected types of compounds have been 

 isolated, and these are now fully described and 

 classified under an improved nomenclature ; but 

 this alone does not explain the advances made in 

 the present book. 



Dr. Armstrong has been quick to realise that 

 the recent recognition of the specially reactive 

 forms of sugars which are regarded as ethylene- 

 oxides has opened out many new fields of inquiry, 

 and has made clear much that has hitherto been 



