232 MICHAEL FARADAY — HIS LIFE AND WORKS. 



to Professor De la Rive,* lie relates all tlie attempts made by liis colla1>orateur 

 and liimself during two years of persevering labor, to discover the most satis- 

 factory alloj^s. He indicates, as one of tlie best, that of rhodium and steel, 

 and, as presenting curious peculiarities, that of steel and silver ; this last alloy 

 does not become a true combination unless the silver only forms one five-lnm- 

 dredth 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 con- 

 struction of cutting-instruments. 



Ahhough interesting in many respects, the results which Faraday obtained 

 in his great inv^estigation 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 researches upon the manufacture of glass for optical pur- 

 poses, whicli he made a few years afterwards, (in 1829.) It was upon the initia- 

 tive taken in 1824 by the Royal Society of London, which named a committee 

 for the study of the improvement of glass with a view to its optical use, that 

 Faraday was called upon to occupy himself with it. Whilst he pursued the 

 chemical part of these investigations, Dollond worked up the glass, and Iler- 

 schel subjected it to the test of experiment. At the end of long and difficult 

 experiments, Faraday ascertained that the greatest difficult}- in the way of the 

 fabrication of a good flint glass (that is to say, a very refractive glass) was the 

 presence of streaks and striae proceeding from a want of homogeneity, due, in 

 its turn^ to differences of composition between the contiguous portions of the 

 same glass. The employment of oxide of lead in the composition of flint glass 

 was the cause of this defectiveness, which could not be avoided even by making 

 use of the most efficacious means of rendering the mixture perfect while in a 

 state of fusion. Among the combinations tried, that of l)orate of lead and silica 

 furnished a glass endowed with optical properties still more strongly marked 

 than those of flint glass, and at the same time presenting a very uniform struc- 

 ture. This glass, which, on account of its great densit}^ (double that of flint 

 glass) has been named heavy glass, is found, unfortunately, to have a slight 

 yellowish coloration, which renders it unfit for optical pinposes ; but the labor 

 which Faraday devoted to its fabrication has not been lost ; for, as we shall see 

 hereafter, this same glass, in the hands of the talented experimenter, became 

 the instrument of one of his most beautiful discoveries. 



In the long and curious memoir which he published upon the fabrication of 

 optical glass, Faraday gives a minute description of all the processes em])loyed 

 by him — of tlie construction of furnaces, selection of crucibles, means of heating, 

 various artifices, such as the injection of platinum in powder into the fused glass 

 to cause the disappearance of buljbles, &:c. It is a genuine instruction in chem- 

 ical manipulation, and, as it were, a complement to his treatise on this subject, 

 which was published in 1827, and has since gone through three editions. Only 

 those who are called upon to experiment in the domains of physics and chem- 

 istry can apjjrcciate the immense service which this treatise has rendered to 

 them, by teaching theni a multitude of processes of detail so valuable for them 

 to know, and of which a description was previously nowdiere to be found, so 

 that every one was obliged to undergo an apprenticeship to them on his own 

 account. It W\as necessary that a savant who for so many years had been strug- 

 gling with the difficulties of experimentation, and who had been able to sur- 

 mount them in so ingenious a manner, should give himself the trouble to 

 describe the means which he had employed, so that his experience might be of 

 service to others. Faraday was this savant, and his object was completely 

 attained. 



Here, pej-liaps, before proceeding to another set of subjects, we ought to 

 speak of certain of Faraday's theoretical ideas relating to general physics, and 

 more especially to the nature of the forces, and their correlation to each other 

 and to the essence of matter ; but we prefer not to discuss the opinions emitted 



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



