6 
accomplished, the mine of knowledge therein contained was so far from being ex¬ 
hausted, that it was merely opened; and when chemical analysis came to be united 
with this optical, or mechanical, resolution of the sun-beam into its colours, it was 
soon found that there were principles there of which the colours, considered 
merely as such, had given no indication. The heat, found most intense without 
the red extremity of the spectrum, and fading away as the other extremity is ap¬ 
proached, was one wonderful step in discovery ; because it shewed that, besides the 
infinite variety of colouring influence in the solar beam, there is an infinite variety 
of another influence, following a different law, and not cognizable by our organs of 
sight. A further step was the power of oxidation at one extremity of the spec¬ 
trum, and the power of deoxidation at the other, which are not discernible to the 
eye like the colours, neither are they palpable to the feeling, or to the thermo¬ 
meter, like the variations of heat. 
This is not the ultimate boundary to which judicious analysis, proceeding cautious¬ 
ly by steps of experience, has already arrived on this most beautiful and truly wonder¬ 
ful subject; for there is a sort of glimmering forecast or belief that all those singular 
effects of the different extremities of the spectrum which are gradual from the one 
extremity to the other, are modifications of two antagonist powers, «as it were, upon 
which every action of Nature depends, or rather in which every action of Nature 
consists. That there is a close connection, and, indeed, an absolute identity, with 
the action of heat, we need not say, for it is felt. On such subjects it requires great 
labour, and still greater care and skill, to arrive at any thing like even mental de¬ 
monstration ; but the probability is that there is a similar identity with those ac¬ 
tions which we call electricity, and galvanism, and magnetism, which seem, in 
truth, to be nothing else than modifications of one general species of action ; for 
when brought to a certain degree of intensity, which has been determined by ex¬ 
periment, their effects are the same ; and identity of effect is the only means that 
we have of believing in identity of cause. Nor is this all; for what we call the 
principal of growth in vegetables, and the principle of life in animals, both of 
which are merely actions, not substances, and actions differently modified under 
different circumstances, we can still trace a striking similarity. Nay, we may 
almost venture upon one step farther, which would join the heavens and the earth 
together in one mighty problem, and furnish us with an instrument of universal 
knowledge, in so far as the material creation and its phenomena are concerned. 
Between those more stubborn energies of the solar beam, which resist most power¬ 
fully the refractive influence of the prism, and that gravitating influence which 
retains the planets in their orbits, there is a most singular, though, in the present 
state of knowledge, a most mysterious, resemblance,—they are both stubborn to 
the line which joins body and body. On the other hand, there is a corresponding 
resemblance between the more yielding or refractive energies, and that orbital 
force which balances the central one, and sustains the planet in its orbit. It is 
