MOSSOTTI ON FRAUXHOFER's RETICULAR SPECTRA. 437 



Following out this idea, I have deduced from Fraunhofer's 

 extremely accurate observations the length of the different parts 

 of the reticular spectrum corresponding to the intervals of the 

 seven principal dark lines pointed out by Fraunhofer. These 

 lines yield so many definite points, to -which the difi'erent parts 

 of the spectrum may be referred ; they are therefore denoted by 

 the letters B, C, D, E, F, G, H, and denominated the principal 

 lines. Fig. 1, Plate II. represents a spectrum of this kind. If 

 this be compared with fig. 2, representing another spectrum 

 which Fraunhofer obtained by refraction by means of his flint- 

 glass prism No. 13*, it will be seen how great the dilFerence is 

 in the extent of the different parts, and how very considerably the 

 refractive spectrum is deformed. The intervals between the prin- 

 cipal lines in the reticular spectrum are respectively expressed 

 by the numbers — 



and in the spectrum produced by refraction — 



13 35 46 40 79 71 



3. The reticular spectrum is characterized by a peculiar pro- 

 perty. In the spectrum formed by refraction, which being 

 larger and brighter allows of more easy observation, Fraunhofer 

 has determined the intensity of the light in those parts which 

 are nearest to the principal lines. The ordinates of the curve, 

 fig. 2, Plate II., represents the intensity of light of the subjacent 

 points of the spectrum. The dotted line jw, between D and E is 

 drawn so as to divide the spectrum into two parts, the quantities 

 (jf light in the different parts in which form two equal sums, or 

 so that it halves the whole light of the spectrum. If in the 

 reticular spectrum a line fx. be drawn between D and E so as 

 to indicate the place w Inch corresponds to the ray j«., it divides 

 the total length of the spectrum into two equal parts. This 

 simplicity of the distribution of the quantity of light in the reti- 

 cular spectrum is a distinctive character of a normal spectrum. 



In the prismatic spectrum the maximum of the intensity of 

 the liglit, which corresponds to the maximum-ordinate of the 

 curve, falls at m, at about /^rths of the interval DE reckoned 

 from D to \i, and is therefore situated beyond the line n* towards 

 the less refractive end of the spectrum. If Ave consider that 



• Dvnkxvliriflen iV.icnd. der Uissenschaften xii Miincheuf. 182.'5. 



