author's abstract of this paper issued 

 bt the bibliographic service, february 23 



STUDIES ON THE RELATIVE PHYSIOLOGICAL VALUE 

 OF SPECTRAL LIGHTS 



II. THE SENSIBILITY OF VOLVOX TO WAVE-LENGTHS OF EQUAL 



ENERGY CONTENT 



HENRY LAURENS AND HENRY D. HOOKER, JR. 



Osborn Zoological and Botanical Laboratories, Yale University 



TWO FIGURES 



INTRODUCTION 



The present paper is one of a series dealing with the deter- 

 mination of the relative stimulating effect of radiation in dif- 

 ferent parts of the spectrum. The experiments to be described 

 were made during the summer of 1917, but due to the pressure 

 of other duties occasioned by the war it has been impossible to 

 prepare the paper for publication until the present time. The 

 work as it is now presented is not complete, delay in the receipt 

 of apparatus has prevented us from continuing the work, and a 

 number of questions are reserved for future investigation. In- 

 complete as the present work is, however, it is considered inad- 

 visable to delay publication longer. A preliminary account of 

 the results has appeared (Laurens and Hooker, '18). 



The determination of the relative visibility of radiation, or 

 the visibility of light of different wave-lengths, consists in find- 

 ing the relation between luminous sensation— 'light' — and 

 radiant energy. The sensibility of the human eye, or the visi- 

 bility of the radiation, at any wave-length is the ratio of the 

 luminous intensity, measured in light units, to the intensity of 

 the light measured in energy units. The curve obtained is the 

 visibility for an equal-energy spectrum. 



The same general procedure can, and should, be applied to 

 the determination of the relative physiological value of light of 



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