MOSSOTTI ON FRAUNHOFER's RETICULAR SPECTRA. 451 



are indirect, appear favourable to the supposition that the dark 

 lines ai-e produced by interference ; hence it is worthy of re- 

 mark, that the line F corresponds only approximatively to the 

 sol, the length of the waves of which is ^^tb less than the length 

 of the strings of the corresponding tone. However, these purely 

 speculative remarks are merely given until we possess more 

 numerous and accurate experimental data. 



Appendix. — On Newton's Theory of the Spectrum. 



If the length of Newton's prismatic spectrum, fig. 3, Plate II., 

 be taken as unity, and the commencement of the coordinates be 

 placed in the outermost point O, at the distance of one of the 

 red boundaries, the abscissae X of the boundaries at which the 

 different colours cease are given by the following numbers : — . 



Xo. Xr. Xa. Xg. Xo. X^ Xi. Xm. 



The letters r, a, g, &c. express respectively the colours red, 

 orange, yellow, &c. 

 Inversely we have 



J_J_J_-LJLJ__LJ_ 



Xo' Xr' Xa" X^' X»' Xt Xi" Xm" 



18539391 



The lengths A. of the fits of the colours corresponding to these 

 limits follow, according to Newton, the numerical values 



Xo. Ar. Aa. Xg. xv. Xt. Xi. Xu. 



(1)1 (f)l (1)1 (i)l (1)1 (1)1 (t%)I (i)f...(2.) 



The extensions of the colours upon the circumference of the 



coloured circle, according to Newton, are proportional to the 



following differences : — 



, Xo , Xr ^ 1 Xa „ 



fr = 1 - xf ; fa = 1 - X^; ^^ = 1 - X^, &c., 



whence we have 



^r. ^a. fy. ^v. ipt. ^i. fu. 



1111 _•_ _1 1 



U TS 10 V 10 iff 9* 



If the circumference of the circle be divided in the proportion 

 of these numbers, the lengths of the curves or,ra, &c. would be 



or. ra. ag. gv. vt. ti. iu. 



60° 45'; 34°11'; 54°4i'; 60° 46'; 54°4l'; 34° 11'; 60° 45'. 



The spectrum represented by this, when rectilinearly extended, 



as in fig. 4, Plate II., would form Newton's normal spectrum. 



The centre of this spectrum would be in the middle of the green ; 



2 H 2 



.(3.) 



