Ae 
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 fora 
good lens five inches in diameter, while it is well known that the con- 
tinental artists have made fine object-glasses from 1 to fifteen inches 
in diameter, and that orders are now sent from Eng and 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 1624, to appoint a commil- 
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 seve inches 
square and eight tenths of an inch thick, tolerably free from bubbles 
and strie. Their glass was a silicated borate of lead, composed 0 
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 ™ 
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 comparativel 
and it is now necessary to revive it, because other branches require 
the aid of improved telescopes and microscopes, to explore the u° 
mensity of space for unseen material systems, and to exam 
nute recesses of matter and its living forms. Our own country 
furnish all the materials in abundance for making the finest glass, @ 
our philosophers and chemists may as well acquire honor and distine 
tion in that direction as in any other. May we not, then, with pro” 
priety and confidence, appeal to the acknowledged genius and pers 
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 
% 
y neglected, 
