64 Various Tints of Autumnat Foliage, [January, 



is only at higher temperatures that the great number of 

 lines in the blue and violet make their appearance, and it is 

 not until the salt is fused that the spectrum becomes con- 

 tinuous. In this case the continuity of the spectrum is not 

 attributed to the diffusion of incandescent particles of the 

 solid substance throughout the flame, but to the widening 

 out of the bands in every part of the spectrum until their 

 fusion produces white light. 



We have to express our thanks to the Editors of the 

 "Journal of the Franklin Institute" and Professor Leeds for 

 this article. At a future time Professor Leeds hopes to 

 replace this preliminary essay by more carefully prepared 

 drawings, and by a more extended table of the lin£s referred 

 in position to normal wave-lengths, and in intensity to the 

 solar spectrum taken as a standard. These further 

 researches, we trust, will, without delay, be communicated 

 to our readers. 



VI. ON THE VARIOUS TINTS^OF AUTUMNAL 



FOLIAGE. 



By H. C. Sorby, F.R.S., &c. 



tN the following paper I shall endeavour to explain the 

 production of all that variety of colour which imparts 

 such a charm to woodland scenery in autumn. I must, 

 however, frankly admit that very much yet remains to be 

 learned. The complete study of the question would involve 

 very much research, and I see the importance of examining 

 the colouring matters in spring and summer now that it is 

 too late. Still, however, I trust that I shall be able to give 

 a tolerably satisfactory general account of the subject, and 

 perhaps little more is desirable on this occasion, since that 

 may interest many who would not care to occupy their time 

 in studying in detail the optical characters of the colouring 

 matters found in leaves. These are certainly very nu- 

 merous, and I have even so far established the existence of 

 about a score, though I have examined only^a few dozen 

 plants with the requisite care. These have, however, been 

 chosen in such a manner as to show the more striking phe- 

 nomena, and probably a more extended examination would 

 merely reveal a greater number of different colours, without 

 materially altering the general results. 



