616 



SCIENCE 



[N. S. Vol. XLV. No. 1172 



tremely able man and that his book contains 

 a great deal of valuable information. The 

 mere fact that it has been through seven Ger- 

 man editions is proof in itself that people read 

 it. There is a fine sound to the subdivisions 

 of the book: the universal properties of 

 matter; atom and molecule; the transforma- 

 tion of matter; the transformation of energy. 

 What could be better than this ? When a man 

 sandwiches a chapter on colloidal solutiond in 

 between one on radioactivity and one on the 

 absolute size of the molecules, one is almost 

 tempted to forgive him for talking about the 

 enormous molecular weights of substances in 

 the colloidal state. In a great many chapters 

 what ISTernst has to say is very well worth 

 while and of course it is not fair to read the 

 parts on colloid chemistry, photochemistry, 

 and flame spectra in the light of what one 

 now knows. It is possibly the war, though I 

 think not; but the whole tone of Nernst's 

 book grates on one, perhaps more when it is 

 presented in English than when one reads it 

 in German. The contrast between this book 

 and van't HofP's Lectures is very striking. 



The translation is very much better done 

 than has been the case in most of the previous 

 English editions. Either the translator or the 

 proofreader has been very careless, however, 

 in regard to proper names, many of which are 

 misspelled. Wilder D. Bancroft 



Cornell Universitt 



SPECIAL ARTICLES 

 THE MEASUREMENT OF LIGHT IN SOME OF 

 ITS MORE IMPORTANT PHYSIOLOG- 

 ICAL ASPECTS 



The principal relations of light to organ- 

 isms include the following phases of its action : 



1. Photosynthesis, in which specialized pro- 

 toplastic masses containing chlorophyll elabo- 

 rate carbohydrates from carbon dioxide and 

 water. The well-known absorption bands of 

 chlorophyll in the red and in the blue are 

 taken to indicate the portions of the spectrum 

 concerned in this action. 



2. Influence of illumination on transpira- 

 tion and water content. It is probable that 

 the red end of the spectrum chiefly furnishes 



the wave-lengths which cause changes in tem- 

 perature, and variations in water loss. 



3. Influence of illumination on the respira- 

 tion and other metabolic processes in proto- 

 plasm as induced by the photolysis of sub- 

 stances important to the life of the organism. 



4. Coagulatory, neutralizing or disinte- 

 grating action of light or toxic effect of prod- 

 ucts, especially of the shorter wave-lengths, on 

 living matter as exemplified by the fatal effects 

 of blue-violet rays on minute organisms. 



5. Tropistio reactions, in which the position 

 of the axes or of the entire body is changed 

 in response to direction or intensity of the 

 rays and with respect to special wave-lengths. 

 Various parts of the spectrum may be active 

 in different organisms. 



6. The indirect action of light on rate, 

 course and amount of growth, together with 

 morphogenic reactions. Such effects have not 

 yet been analyzed to an extent which might 

 furnish data for a rational discussion of the 

 direct effects of light on growth. Indirect 

 effects are recognizable. 



7. Action of light on environic conditions 

 exemplified in the ionization of the air by the 

 shorter wave-lengths as described by Spoehr. 



Experimentation upon any of these subjects 

 requires sources of light under good control, 

 screens for transmitting special regions of the 

 spectrum and methods of measurement of the 

 relative intensity of the illumination falling 

 on the organism. 



Sunlight may serve in some work when the 

 requisite screens are available, but incandes- 

 cent filaments, mercury and amalgam vapor 

 arcs enclosed in glass or in quartz may be 

 used as sources of light down to wave-lengths 

 of .28 ,^. 



Layers of liquid, pigments in gelatine and 

 other perishable screens have served admirably 

 in some demonstration and research work, but 

 when long-continued exposures to intensities 

 approaching those of normal sunlight are de- 

 sired a durable screen is necessary. A series 

 of formulffi for a number of glasses which 

 would transmit various parts of the spectrum 

 has been developed in the laboratory of a 

 prominent firm of glass-makers. These may 



