Photographic Investigation of Spectra of Chlorophyll, $c. 389 



When a is small, sin 2a = tan 2x = r , 



A. 



R 2 = v/(A 2 -f WB 2 ) = A, approximately. 



-IT ft-aB 



Hence p = \/ A -f t - rr- 



*/ A. 



Here nj&f/h. is the coefficient of absorption of the solution, and is 

 proportional to n 2 , the number of molecules of the absorbent substance 

 present per unit volume. Since it is essential that (19) should 

 possess a well-marked maximum value for a certain wave-length (that 

 of the light absorbed), additional evidence is obtained in support of 

 the introduction of a viscous term into the equations to the atomic 

 vibrations. 



The equation for the square of the refractive index of a substance 

 like crystallized copper sulphate, which possesses marked selective 

 absorption without exhibiting selective reflection to any extent, 

 might be represented by an equation of the form of (18) ; r 2 , &c., 

 now referring to the conditions of motion of a particular atom, the 

 motions of the remaining atoms giving rise to the terms involving 

 T,, Ac. 



" A Photographic Investigation of the Absorption Spectra of 

 Chlorophyll and its Derivatives in the Violet and Ultra- 

 violet Region of the Spectrum." By C. A. ScHUNCK. 

 Communicated by Dr. E. SCHUNCK, F.R.S. Received 

 March 17, Read March 24, 1898. 



[PLATES 3, 4, 5.] 



As is well known from the investigations of Soret,* Gamgee,f and 

 others, haemoglobin and its coloured derivatives show a character- 

 istic absorption band lying between the lines Gr and M of the solar 

 spectrum. The band has been shown to vary in position between 

 narrow limits ; in some derivatives it is nearer the red, and in others 

 nearer the violet, end of the spectrum, and is of all the blood absorp- 

 tion bands the most stable. 



The very near relationship that has been shown <o exist by Schnnck 

 and MarchlewskiJ between phylloporpbyrin (a chlorophyll deriva- 

 tive) and haematoporphyrin (a haemoglobin derivative), and the 

 remarkable resemblance of their absorption spectra one may almost 



* ' Arch, des Sciences Phys. et Nat.,' vol. 61, p. 322 ; vol. 66, p. 429. 

 f 'Arch, des Sciences Phys. et Nat.,' Dec., 1895. 

 J ' Roy. Soc. Proc.,' vol. 59, p. 233. 

 VOL. LXIH. 2 G 



