EMPIRICAL KNOWLEDGE, EXPLANATION, <kc. 161 



only two sensibly translucent metals 1 Why should 

 sulphur be capable of so many peculiar changes into 

 amorphous conditions ? 



There are whole branches of chemical knowledge which 

 are as yet mere aggregates of disconnected facts. The 

 properties of alloys, or mixtures of metals, are often ex- 

 ceedingly remarkable ; but no laws have yet been detected, 

 and the usual laws of combining proportions seem to have 

 no clear application e . Not the slightest explanation can 

 be given of the wonderful variations of the qualities of 

 iron, according as it contains more or less carbon and 

 silicon, nay, even the facts of the case are often involved 

 in uncertainty. Why, again, should the properties of 

 steel be remarkably affected by the presence of a little 

 tungsten. All that was determined by Matthiessen con- 

 cerning the variation of the conducting powers of copper 

 according to its purity, was of a purely empirical cha- 

 racter f. Many animal substances cannot be shown to obey 

 even the laws of combining proportions. Thus for the 

 most part chemistry is yet a science occupied with an 

 exact description of artificial or natural substances, which 

 by the collection of enormous numbers of exact facts 

 is preparing the way for an extension of theory at some 

 future time. 



We must not indeed suppose that any science will ever 

 entirely cease to be empirical. Multitudes of phenomena 

 have been explained by the undulatory theory of light ; 

 but there remains an almost undiminished mass of facts 

 yet to be treated. The natural colours of bodies, and the 

 rays given off by them when heated, are yet free from all 

 theory, and yield few empirical coincidences. The theory 

 of electricity is partially understood, but the conditions 

 of the production of frictional electricity defy law or ex- 



e 'Life of Faraday/ vol. ii. p. 104. 

 f Watts, 'Dictionary of Chemistry/ vol. ii. p. 39, &c. 

 VOL. II. M 



