The two reflecting telescopes now submitted by the subscriber, are constructed on the plan of Sir William Herschel, having the front view. The largest has a focal length of 9½ feet; the diameter of the speculum is 8½ inches, and has five astronomical eye-pieces, and one terrestrial eye-piece, for showing objects erect; the lowest power is 57, the highest 900. The smallest has a focal length of 7 feet 9 inches; the diameter of the speculum is 6½ inches, and has one terrestrial, and four astronomical, eye-pieces; the lowest power is 60, the highest is 600. They are of the same kind as those that were submitted a year ago, except the manner of mounting, which is very different.
Amasa Holcomb.
On the evening of the 4th of May, the committee met, by appointment, in an open lot south of the Pennsylvania Hospital, for the purpose of testing the performance of the telescopes, which had previously been tried by some of the members of the committee, and by other gentlemen, on the evening of the 2d. The result of the examination was highly creditable to Mr. Holcomb, and cannot fail to gratify all who have at heart the advancement of astronomical science in this country.
The instruments, with powers varying from 50 to 600 in the smaller, and to 900 in the larger, gave satisfactory views of the moon with a sufficiency of light.
Mr. Holcomb’s ability to manufacture telescopes which should bear a comparison, on favourable terms, with the best four and five feet achromatics now in the country, having been established by the report of the committee in May, 1834, their attention was chiefly directed to ascertaining the degree of perfection to which he has attained in his art, by his persevering efforts during the past year. Accordingly, the remarks which follow are made with reference to the larger telescope, of about ten feet focal length, eight inches aperture, and with a positive eye-piece, giving a power of about 900, and the surface of the field of view nearly twice as great as that of a Gregorian, and one-third greater than that of an achromatic telescope, under similar circumstances.
The view of the moon with its rugged surface, its ridges of mountains, and the endless variety of indentations on its surface, was interesting beyond description, and exceeded any thing of the kind the committee have ever witnessed.
Saturn’s ring, though not in a favourable position, was seen manifestly double, for the first time in this country, as far as the information of the committee extends.
The companion of Polaris appeared as a star of the fourth or fifth magnitude, to the unassisted eye.
The double stars, Castor, μ Draconis, 4 and 5 ε Lyræ, and 44 Bootes, were distinctly separated, and the dark space between them made evident. The last mentioned, consisting of two stars of the fifth magnitude, distant 3″ made a fine appearance; they were soft, and well defined, and there were no scattering rays of light, as was the case with Castor, in both instruments.