444 MOSSOTTi ON frauniiofer's reticular spectra. 



the corresponding parts of the spectrum, is proportional to the 



dx 

 differential coefficients -—, so that when G signifies the inten- 



W A 



slty of the light at the point x in the prismatic spectrum, Tmust 

 correspond to the point A in the reticular spectrum : 



^ = »ll«' (^o 



in Mhich ?z is a constant coefficient. 



cl X 

 The value of the differential coefficient -r— is found from the 



(IK 



equation (1.), Avhich when differentiated yields 



^': = _ i fioV \h + oj, (Mn ^Mi 



ciX Aq \ A / L \ A / J sin i (<^ + ;{/ + 0?) ' 



whence 



^&y['--(^»y] 



Aq \A/ L \A / J sin ^ ($ + ;!; + .r) 



If tlie above mean values be substituted for G, and the data 

 in the preceding paragraph for Aq, A, x, f, 4/, we obtain the fol- 

 lowing values of — r for the positions of the principal lines: — 



B. C. D. E. F. G. II. 



9054; 30851; 294375; 315787; 145931; 39316; 9471. 



These numbers give the ratios of the Intensities of the light 

 of the reticular spectrum at the points mentioned. 



§ III. On the Curve formed by the Intensity of the Light in the 

 various parts of the Reticular Spectrum, 



5. Since the intensities of the light of different parts of the 

 spectrum are recognised by means of the eye, they must depend 

 both upon the amount of rays accumulated at one part, and upon 

 the susceptibility of the retina for the peculiar species of those 

 rays. The law cf the vai'iability of this intensity, being dependent 

 upon both pliy:)ical and physiological elements, is too comjolicated 

 to allow of its being deduced a priori in the present state of our 

 knowledo-e. However, as we have already determined the pro- 

 portions of the intensities of the light in the various parts of the 

 reticular spectrum, we may seek a posteriori for a formula which 

 connects them by a law of continuity witli each other, and thus 

 renders their properties more intelligible. 



