34 T/ztf Action of Light upon the [January, 
If we carefully trace the instances in which both faCts are 
imperfectly ascertained, and laws accepted or rejected with- 
out full verification, we shall feel that a new SPepsis Scientifca 
is urgently demanded in the present day. 
III. THE ACTION OF LIGHT 
UPON THE 
COLOURATION OF THE ORGANIC WORLD. 
NTIL the earlier portion of the present century light, 
by the vast majority of civilised persons, was re- 
garded as a medium for the sense of sight, and as 
very little more. With the discovery of its chemical func- 
tions, brought home to the popular mind by the invention 
of photography, a revolution in opinion took place, and the 
danger now is, not that its real powers should be overlooked, 
but that it should be credited with effects in which its part 
is very doubtful. It has been especially proclaimed to be at 
once the creator and the destroyer of colouration in the 
organic world. The superior intensity of the light to which 
they are exposed has been pronounced the chief cause why 
diurnal species are more gaily coloured than their nearest 
nocturnal allies, and why the flora and the fauna — especially 
the inserts and the birds — of tropical regions are so rich in 
hues of a gorgeous character. It may therefore be not un- 
interesting to inquire into this supposed double function of 
light, and ascertain, if possible, its limits in either direction. 
In so doing it will be impossible for us to overlook the views 
put forward by Mr. A. R. Wallace in a recent issue of 
“ Macmillan’s Magazine.” 
The bleaching power of the sun’s rays, and to a less 
extent of ordinary diffused daylight, has been fully recognised 
in the affairs of daily life. It has been observed that this 
same agency, utilised formerly in preparing vegetable fibre 
for the reception of colours, gradually destroys, in almost 
every instance, the work of the dyer and the printer, and 
exerts a corresponding influence upon the hues of plants. 
There is, however, a distinction by which its effects upon 
the integuments of animals are limited. 
