28 THE PROGRESS AND SPIRIT OF 



new facts and presumptions unceasingly offer themselves,, the 

 foundation and materials of more exact knowledge. Omit- 

 ting gravitation, which we have already denoted as a special 

 power in the material universe, there comes that wonderful 

 element of Light ; blending itself, as we have seen, with heat, 

 electricity, magnetism, and chemical affinity, in such close 

 co-relation of action that we can scarcely dissever its conti- 

 nuity, or detach these physical forces from connection with 

 that great source whence light itself chiefly emanates. The 

 solar beam, as unfolded and analysed in the spectrum, is in 

 truth the most marvellous and mysterious object of the phy- 

 sical world; comprising in itself whole volumes of science, 

 and problems that might put to trial the boldest theorist. 

 The poetry of Milton, sublime though it be, fails to reach 

 the reality of these great attributes of light, as evolved from 

 a single beam, by simple refraction in passing through a glass 

 prism. It is an analysis of exquisite order and perfection ; 

 in which not only are the several colours separated in the 

 same constant proportions, with the intervention of numerous 

 dark lines equally constant in their character; but rays of 

 heat and of chemical power appear severally also at opposite 

 extremities of the spectrum, partially interblended with those 

 of colour, but in greatest intensity beyond the visible co- 

 loured limits of the spectrum. We are now speaking only of 

 the simplest relations of the solar light to terrestrial matter ; 

 and without any immediate reference to the phenomena in- 

 cluded under the undulatory theory of light, which, though 

 attested by mathematicians, and interpreted by numbers, 

 wholly transcend the powers of human conception. We 

 allude, but cannot here do more than allude, to those formula 

 of space and time expressing the amplitude and frequency of 

 the undulations, and their variations for the several colours 

 and rays of the spectrum ; and the whole series of phenomena 

 of transmission, refraction, polarisation, and interference of 



