380 Notices respecting Neiv Books. 



and follows exactly the cosine curve assumed in the previous 

 theoretical discussion o£ the flicker photometer. 



2. By the use of this photometer it has been possible to 

 verify in exact quantitative manner the relationships be- 

 tween relative intensity and absolute intensity of compared 

 fields and critical speeds, as previously calculated from 

 theory. 



3. Measurements have been made of the brightness and 

 hue discrimination fractions for both steady and fluctuating 

 impressions. 



4. It has been found that the applicability of the flicker 

 photometer to colour difference comparisons is due to the 

 failure of hue discrimination as compared with brightness 

 discrimination under conditions of rapid fluctuation, and 

 the amount of this failure has been determined by 

 measurement. 



5. A complete expression has been worked out for the 

 behaviour of the flicker photometer in terms of the critical 

 frequency-illumination relations for the two compared 

 colours, and the hue discrimination fraction for fluctuating 

 impressions. 



I am greatly indebted to Mr. E. R. Morton for assistance 

 in the construction of the experimental apparatus and in 

 making the readings, and also to Mr. Kingsbury and 

 Dr. Karrer for the series of observations made by them. 



Physical Laboratory, 



The United Gas Improvement Company, 



Philadelphia, Pa. 

 September 13th, 1916. 



XXXVII. Notices respecting New Books. 



Annuaire pour Van 1917 publie par U Bureau des Longitudes. 

 Paris : Gauthier-Villars. Price 2 fr. net. 



T1TITH very little delay appears this useful annual publication as 

 * » though the world were at peace. Besides the usual astro- 

 nomical tables there appear in this issue chapters on Metrology 

 and Meteorology, besides special articles on (A) the Babylonian 

 calendar, (B) summer-time 1916 by J. Eenaud, (C) determi- 

 nation of the metre in terms of wave-lengths of light, by 

 M. Hamy. 



The article on summer-time, in particular, is of great historic 

 interest in the summary it gives of the debates which took place in 

 France and elsewhere prior to making this salutary change. 



