376 On the component Parts of Light, 
phorescent bodies would appear to prove conclusively, that each 
coloured ray contains the component parts of every other, Some 
of these bodies, when exposed to light, are capable of absorbing 
it to a considerable extent, and again emitting it in the dark 3 and 
this, for any number of times.. The light which each of them 
emits, is always of the same colour; and this colour it absorbs 
and emits to whatever coloured ray it may be expesed; so that 
from every coloured light it is able to obtain light of its own co- 
Jour. This seems hardly capable of explanation, except upon 
the supposition that the coloured rays are not homogeneous, but 
are capable of decomposition by the different attraction of bo- 
dies. , 
That this is possible, is further confirmed by the fact, that 
light of one colour may be formed by the combination of two 
other differently coloured ravs of light. Thus the blue and yel- 
low rays combined, form green rays, This could not be the case 
if the green were homogeneous; but if the colour arise from the 
proportions ef the calorific and chemical substances, it would ne- 
cessarilyfollow,that if a kind of light containing an excess of one 
of the ethereal matters should be mingled with another kind of 
light, containing an excess of the other, the combined: light 
would be of an intermediate kind, and accordant in its naturé 
with that which, from other causes, contained similar proportions. 
If the hypothesis before mentioned be just, it should explain 
the other phenomena of colour; and the degree of ease and cor- 
rectness with which it does so, will form the surest test of its 
truth. 
Sir Isaac Newton proved, that bodies attracted the whole so- 
lar ray; and as the ray is not bound together by attraction of 
cohesion, they must attract every part, and consequently both 
the calorific and chemical rays. They do not, however, attract 
them with the same force. This is evident, from the different 
chemical influevces of the two rays, which must arise from the 
different degrees of attraction for different substances. But if 
bodies attract both kinds of ethereal matter, and in different pro- 
portions, if they should be placed in an atmosphere containing 
an excess of both, they will attract, and consequently reflect both, 
i quantities proportioned to their attractions*. The combi> 
‘ nation 
* This is probably liable to some modifications, from a well-known dif- 
ference in the energy of the two rays ; particularly in those substances, of 
which the colours seem in some degree to change with the degree of ligh\ 
The calorific ray is less impeded by opposition to its progress, than the che- 
mical ray. It is less easily reflected, less refrangible, less stopped by a 
misty atmosphere. It is possible therefore, that from this cause, in some 
cases, exactly the same proportions which are attracted may not be reflected. 
This different energy may perhaps be accounted for, by supposing pe i 
: DD. Gane «eaieeaie 
