and the Cause of Colour. We 
Light produces the same chemical effects which are attributed 
to caloric; indeed a property always ascribed to light is, that it 
occasions a rise in the temperature. Some effects, however, are, 
usually esteemed peculiar to the operation of light, as distinct 
from its action in producing heat. This may easily be explain- 
ed, by presuming a circumstance very probable to be the fact, 
which is, that the ethereal fluid commonly afforded to the cru- 
cible or retort, may be compounded of proportions different from 
those contained ia the solar beam. This is confirmed by the ex- 
periments of Count Rumford, who found that many of the effects 
usually attributed to the peculiar operation of light as distinct 
from caloric, may be produced in an oven, probably from the 
difrerence in the nature of the heat *. 
On this hypothesis, chemical decompositions will take place, 
either from one of the component parts of the body combining 
with the ethereal matter with more force than with the other 
component parts; or from the attraction of the different com- 
ponent parts being for dissimilar proportions of the ethereal 
fluid, and with an intensity greater than that with which the parts 
attract each other. And possibly the influence of these combined, 
attractions, which always operate in chemical combinations, de- 
cides, in a considerable degree, those specific proportions in which 
other bodies are particularly disposed to unite; it being evident, 
thatif a fourth substance be added to three others for which it 
has a chemical affinity, the proportion in which it will be most 
disposed to combine, cannot be produced by an attraction which 
it has for one, but must depend upon the proportionate attrac- 
tion which it has for each, and which they have for each other. 
To put, as an example, one of the simplest cases. If two sub- 
stances, having a chemical affinity for each other, should attract 
the same proportions of the ethereal fluids, but one should attract 
them with double the force of the attraction in the other, the in- 
fluence of ‘the ethereal fluids would be, to induce a tendency in 
the bases to combine in proportions as one to two. if one par- 
ticle of one substance should attract the two fluids with forces 
as four and two, anda particle of the other with forces as six 
and three, three particles of the first would attract them with 
forces as twelve and six, audtwo particles of the other would at- 
tract them with the same forces: consequently, the same quan- 
tity of the ethereal fluids would attract three particles of one of 
the bases, with the same force with which it would attract two 
particles of the other; and, according to the general laws of tem 
perature, which produces an equalization of the acting force of 
attraction in all bodies, it would tend to cause their combination 
in the proportions of three and two. 
* Philosophical Transactions. 
Aa3 But 
