V2 
Ghe Chenrical Action of Light. 
By G: (Harris: Morris, Pa-D., CS. SEG: 
(Read before the Society, March 17th, 1893.) 
[CONDENSED. | 
"AI\OME few months since the two leading professors of 
chemistry in Germany were engaged in a vigorous 
controversy concerning the derivatives of two little- 
known acids, namely, tiglic acid and angelic acid. 
The point in dispute was an important one, as affecting the con- 
stitution of these acids, and was purely experimental: the one 
worker maintaining that certain compounds could be obtained 
from the acids, whilst the other asserted his inability to prepare 
these compounds. Eventually the solution was found in the fact 
that the former worked in comparative darkness and the latter in 
full daylight, and that under the influence of light the derivatives 
in question were decomposed as fast as they were formed. 
Hence the difference in the results obtained. 
This incident serves as a fitting introduction to the subject 
which I wish to bring before you to-night. In it we have an 
instance of the all-pervading influence of the chemical action of 
light, which is as essential to the well-being of the world as is 
air or water. The green foliage of the trees, the bright hues of 
the flowers, the strength and health of mankind, are all due to 
its beneficent influence. The stimulating action of light not being 
of such obvious universal necessity to vital action as that of 
heat ; nor its effects and influence so prominently marked, its full 
power as an excitant upon animal and vegetable life was not so 
quickly and readily recognised ; but now it is universally admitted 
