416 Prof. A. de la "Rive's. Memoir of 



to light, published by Faraday in 1857. Among other interest- 

 ing facts that this memoir contains, we shall cite that of a leaf 

 of beaten gold, which, when placed upon a plate of glass, becomes 

 perfectly transparent and colourless when it is brought to a high 

 temperature, and which, when seen by transmitted light, resumes 

 its green colour when it is subjected to strong pressure. A 

 great number of experiments upon the pulverulent deposits of 

 various metals obtained by electrical discharges transmitted 

 through very fine wires, led to remarkable results as to the va- 

 riations of colour arising from change in the molecular state of 

 the same body. We also find in this memoir a detailed investi- 

 gation of the various colours presented by different solutions of 

 gold, and especially of the fine ruby-red tinge obtained by the 

 solution of a quantity of gold which, if agglomerated into a 

 single mass, would not occupy the seven-hundred-thousandth 

 part of the volume of water which it colours. It is not neces- 

 sary to dwell upon the interest presented by researches having 

 for their object the study of the influence, still so imperfectly 

 known, of the molecular structure of bodies upon their relations 

 to light, and especially upon their transparency. 



Among the numerous works of Faraday relating to the appli- 

 cations of science to the arts, we shall confine ourselves to citing 

 his researches upon the manufacture of steel, and of glass for 

 optical purposes, these being the most important. 



It was by the analysis of the Indian steel called wootz that he 

 was led, in concert with Stodart, to compose an alloy which had 

 all the properties of this, by combining aluminium with iron and 

 carbon. In a letter addressed in 1820 to Professor De la Rive*, 

 he relates all the attempts made by his collaborateur and himself 

 during two years of persevering labour, to discover the most sa- 

 tisfactory alloys. He indicates, as one of the best, that of rho- 

 dium and steel, and, as presenting curious peculiarities, that of 

 steel and silver ; this last alloy does not become a true combina- 

 tion unless the silver only forms ^q part of it. Platinum, 

 on the contrary, combines in all proportions with steel, but it 

 does not furnish so good an alloy as rhodium and silver for the 

 construction of cutting-instruments. 



Although interesting in many respects, the results which Fa- 

 raday obtained in his great investigation of the alloys of steel 

 were not proportionate in their importance to the time and trouble 

 which they cost him. We may say the same of the laborious re- 

 searches upon the manufacture of glass for optical purposes, which 

 he made a few years afterwards (in 1829). It was upon the 

 initiative taken in 1824 by the Royal Society of London, which 

 named a committee for the study of the improvement of glass 

 * See Bibl. Univ. (1820) vol. xiv. p. 209. 



