PHYSICAL NATURE OF ANIMAL LIGHT 



59 



firefly." This is calculated to be .02 watts per candle. 

 More recent determinations (Coblentz, 1912), using a new 

 sensibility curve of Nutting's (1911) for a partially light- 

 adapted eye, give the reduced luminous efficiency as 87 



396^ 430.8 

 4 0g .'" . . }° 



FR/MJNHOFER LINES. 

 6S6.S 687J> 7li.S TiO. 



WAVC-LENOTH, METERS . I«"' 



Fig. 15. — Spectral energy, luminosity and visibility curves (.after Oibson and McNicholat) 



A. Spectral energy curve of Hefner lamp. 



B. Spectral energy curve of acetylene flame. 



C. Spectral energy curve of tungsten (gas-filled) glow lamp. 



D. Spectral energy curve of black body at 3000° absolute (sunlight). 



E. Spectral energy curve of blue sky. 



Hff. Spectral energy curve of Hereeus quarts mercury lamp. 

 Lt Visibilitjr curve for human eye. 

 La. Luminosity of Hefner lamp. 

 Le. Luminosity of blue sky. 



per cent, iov Photinus pyralis, 80 per cent, for Pho- 

 tinus consanguineus and 92 per cent, for Photuris 

 pennsylvanica. 



The luminous efficiencies of various forms of artificial 

 illuminants have been calculated by Ives (1915) and are 

 given together with that of the firefly in Table 6. Fig. 15 



