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 A what we call the 

 principle 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 



