62 ARTICLES REFERRED TO IN THE SECRETARY'S REPORT, 
DRAPER’S TELESCOPE. 
BY THE REV. T. W. WEBB, A.M., F.RJA.S. 
From the ‘‘ Intellectual Obserzcr,’’ London. 
It is gratifying to observe that, amidst all the calamities and distresses and 
contusion of a most unhappy civil war, the studies of peace have not been 
wholly lost to sight. A remarkable instance of this is afforded by the recent 
appearance, among the publications of the American Smithsonian Institution, 
of a very interesting and valuable memoir, “On the Construction of a Silvered 
Glass Telescope, 154 inches in aperture, and its use in celestial photography, 
by Henry Draper, M.D., Professor of Natural Science in the University of New 
York.” <A copy of this, through the courtesy of the author, being now in my 
hands, I have thought that some account of its contents might prove interesting, 
especially at a time when silvered glass specula are attracting some attention in 
England, and (unless we are much mistaken) are likely to be more generally 
known and valued as most important aids to the progress of observation. 
The opening sentence of this memoir requires, however, we venture to think, 
a little qualification. “The construction of a reflecting telescope capable of 
_ showing every celestial object now known,” Dr. Draper tells us, ‘“ is not a very 
difficult task.” We should have no hesitation in expunging the negative here, 
unless it were permitted to add, “when study, and labor, and ingenuity, and 
perseverance have been brought to bear upon it, equal to those displayed by 
Dr. Draper.” His subsequent remark is of more universal application: “The 
cost of materials is but trifling compared with the result obtained; and I can 
see no reason why silvered glass instruments should not come into general use 
among amateurs. ‘The future hopes of astronomy lie in the multitude of ob- 
servers, and in the concentration of the action of many minds.” His first idea 
was derived from an examination, in 1857, of Lord Rosse’s great reflector, and 
of the machinery by which it was perfected; and on his return home in the 
following year, he resolved to construct a similar, though smaller instrument, 
larger, however, than any in America, and adapted to celestial photography. 
A metal speculum was first completed, but was split in two during the winter 
of 1860 by the expansion of a few drops of water that became frozen in the 
supporting case ; and his attention was then, at Sir John Herschel’s suggestion, 
turned to silvered glass mirrors, as reflecting more than 90 per cent. of incident 
light, with only gth of the weight of metal. The year 1861 was occupied in 
overcoming the difficulties of grinding and polishing three 154-inch disks of 
glass, as well as a variety of smaller pieces. Three similar mirrers were found 
almost essential, as two would often be so much alike that a third was necessary 
to ghin a further step in advance. One was made to acquire a parabolic figure, 
(see INTELLECTUAL OBSERVER, iii, 213,) and bore a power of 1000. The 
winter was spent in perfecting the art of silvering and studying photographie 
