430 



Prof. C. Timiriazeff. 



[Apr. 30, 



of its nearest products had to be studied more thoroughly than they 

 had been. It would lead me too far out of the way if I were to give 

 an account of my researches published in a small Russian volume in 

 1871. My plates represent an attempt at a classification of chloro- 

 phyll and its products based on their spectroscopic characters, an 

 attempt that seems to me fully confirmed by the more recent and 

 detailed researches, especially of the late Mr. Edward Schunck, of 

 Marchlevsky, and of Professor Hartley. I will pause for one moment on 

 the method of representing the spectra which I adopted at the time and 

 have since been trying to improve. Till then the spectrum was 

 generally represented as consisting of distinct black bands separated by 

 bright intervals, and it corresponded to a certain more or less arbitrary 

 state of concentration or thickness of layer. Plotting together whole 

 series of spectra corresponding to layers of varying thickness, I obtained 

 the following spectrograms. At a later period I substituted, for a 

 somewhat troublesome method, the direct inspection of the solutions in 

 wedge-shaped troughs a method, if I am not mistaken, introduced by 

 the late Professor Gladstone and lastly contrived to obtain directly 

 these spectrophotograms. It is a curious fact, to be mentioned 

 en passant, that so far as I know photography has till now been 

 applied only to the more refrangible and not to the less refrangible 

 part of the spectrum of chlorophyll, which is of the highest interest to 

 the botanist. 



Here are some photographs that I obtained, in 1 892 (fig. 2), on 

 ordinary Ilford plates, which were also used for the first spectrophoto- 



FIG. 2. 



Photographic Spectrum of Chlorophyll. 



i. i. m. w. 



Modified Chlorophyll (Stokes), sain e| Con cent rat ion. 



