18 
ANNIVERSARY ADDRESS. 
magenta, have impressed upon tliem by superhuman decree the power 
of similarly decomposing light and yielding colour. Tor, be it 
observed, colour is a property of the light which shines on 
substances and not of the substances themselves; or, as Hill 
poetically expresses it, “ light is the pencil with which God paints 
in all the hues of creation.” Thus we say the grass is green, while 
the fact is that every blade contains a certain substance which 
has the power given to it of decomposing white light and of 
absorbing most of the resulting colours but of reflecting the 
green rays. The green rays of the original white beam of 
light are just those which are not taken up by the leaf; they 
no sooner impinge on the leaf than they are reflected away 
from the leaf and some of them entering the eye of an observer 
produce the effect of greenness. Thus regarded, the leaf itself is 
anything but green. But if by greenness we mean that the leaf 
has the power of reflecting green light, then the leaf is rightly 
termed green. Certain other properties of spectra are derived 
from special elementary metals and other elements in a state of 
incandescence ; hence when these properties present themselves 
in the light of, for example, the sun, the necessary conclusion 
is that those metals or elements are present in the sun—and even 
in the stars and in the irresolvable nebula?. 
But the laws which rule in interstellar space or even in our 
solar system cannot be further considered within the limits of an 
anniversary address. The laws of heat are as striking and all¬ 
ruling as those of light, can equally easily be grasped by man, 
and can be expressed in similar human language. The force of 
heat is radiated, reflected, and refracted under similar laws to 
those just stated for light. These simple laws govern the heat 
which is generated within our systems by the burning of our 
food, and the heat yielded by our fires and flames, no less than 
they govern the heat which, radiating in every direction from the 
sun, necessarily yields a few rays to that speck in space which is so 
dear to us and which we call Our Earth. Were the laws of heat 
better understood by the denizens of that planet, they would 
commit fewer mistakes in the matter of clothing by night and by 
day, in summer and in winter, fewer in the warming of their 
public edifices or their private dwellings. 
Erom a consideration of the laws governing the force which 
penetrates the eye and thus enables man to see—the laws of light 
—and from an allusion to the laws governing the kindred force 
which penetrates every part of the skin and affects every part of 
the animal frame—the laws of heat—it would be appropriate to 
