104 THE NEW WORLD OF SCIENCE 



made to introduce new glass fluxes, and effort was expended 

 only in perfecting technical manipulation and adding to the list 

 of dense flints. 



To this state of affairs there were, however, a few notable 

 exceptions : Frauenhof er, the German optician ; Faraday, the 

 great investigator; and Harcourt, an English clergyman. 

 Frauenhofer succeeded in finding glass which showed a diminu- 

 tion of the secondary spectrum, but the new glass was not 

 produced on a commercial basis and the formula was unfor- 

 tunately completely lost. In 1825 Faraday was appointed by 

 the Royal Society, together with Sir John Herschel and Mr. 

 Dolland, on a committee to examine, and if possible, to improve 

 the manufacture of optical glass. The results of the systematic 

 and very exhaustive experiments were reported, minutely by 

 Faraday in 1829, and although glass so found did not prove to 

 be of important practical use, yet the work performed had 

 much directional influence on subsequent researches. 



Harcourt could not obtain from his small meltings pieces of 

 sufficient size and perfection to permit a complete spectrometric 

 analysis, and lacking information which could be gained only 

 with the spectrometer, his subsequent work suffered for want of 

 guiding experience. However, these researches were not 

 entirely in vain, since certain facts were established relating to 

 the effect of some chemical elements upon the refraction of 

 light. 



Until the late seventies silicon, sodium, potassium, calcium, 

 lead, and oxygen had been the only elements used, excepting 

 perhaps alumina and thallium in an experimental way. Crown 

 and flint glasses were being produced of a far better quality 

 as regards clearness, freedom of color, and homogeneity, and 

 flint of far greater refractive power and dispersion, than had 

 been offered up to this time. 



In the late seventies Professor Ernest Abbe of the Univer- 

 sity of Jena published a paper on the microscope, in which he 

 made an appeal to scientists to take up the improvement of 

 optical glass, and pointed out that scientific instruments were in 



