208 Miscellanies. 



others, has been gradually improving ; and for common purposes of 

 life, the best flint glass now made, exhibits a transparency and beauty 

 which leaves little to be expected from future improvement. But the 

 present state of the arts and sciences requires the greatest attainable 

 perfection in optical instruments, and their glass lenses should possess 

 not only perfect transparency, but perfect homogeneity, so as to 

 produce the least possible irregularity of refraction and dispersion. 

 The invention of the achromatic object-glass, composed of two or 

 more lenses of different kinds of glass, probably induced the English 

 glass-makers to make experiments to improve the manufacture ; but 

 it has since declined, or at least has not improved in proportion to the 

 progress of the other arts in England, and Mr. Dollond acknowledged 

 that he had not, for ten years, been able to procure flint glass fit for a 

 good lens five inches in diameter, while it is we\\ known that the con- 

 tinental artists have made fine object-glasses from ten to fifteen inches 

 in diameter, and that orders are now sent from England to the conti- 

 nent for the largest and finest instruments used in astronomical obser- 

 vations. This apparent decline in one of the most useful arts, induced 

 the Royal Society of London, in the year 1824, to appoint a commit- 

 tee of its members and the members of the Board of Longitude, for 

 the improvement of glass for optical purposes. This committee ap- 

 pointed a sub-committee, consisting of Sir John Herschel, Mr. Dol- 

 lond, and Dr. Faraday. These gentlemen, most eminent in science, 

 conducted all the experiments, and in the year 1834 reported prog- 

 ress, and that they had succeeded in making glass plates seven inches 

 square and eight tenths of an inch thick, tolerably free from bubbles 

 and striae. Their glass was a silicated borate of lead, composed of 

 104^ parts of nitrate of lead, 24 parts of silicated lead, and 42 parts 

 of borax ; specific gravity 5.44, refractive index 1.8735, dispersive in- 

 dex 0.0703; and was not free from color. This result does not ap- 

 pear to have been very satisfactory, and I have not heard of any fur- 

 ther experiments or results. 



This branch of physical science has been comparatively neglected, 

 and it is now necessary to revive it, because other branches require 

 the aid of improved telescopes and microscopes, to explore the im- 

 mensity of space for unseen material systems, and to examine the mi- 

 nute recesses of matter and its living forms. Our own country will 

 furnish all the materials in abundance for making the finest glass, and 

 our philosophers and chemists may as well acquire honor and distinc- 

 tion in that direction as in any other. May we not, then, with pro- 

 priety and confidence, appeal to the acknowledged genius and perse- 

 verance of our citizens, for a share of their attention to this subject ; 

 and in this view of it I beg leave to submit a few desultory remarks, 



