That the following is the description of the instrument as given by Mr.
Holcomb.
“The telescope submitted to the examination of the Committee
of the Franklin Institute is of the reflecting kind; has a
focal length of six feet; the diameter of the speculum is three
inches nine-tenths; the rays of light are reflected but once;
the image formed in the focus of the speculum is viewed by a
common astronomical eye piece, or by a single lens; it has
also an eye piece for viewing land objects, which shows them
erect. The telescope is of the same construction as those of
Sir William Herschell, the observer having his back towards
the object and looking directly towards the speculum. It has
an advantage over those of the Gregorian and Newtonian forms,
by showing the object brighter with the same aperture, there
being no light lost by a second reflection. The diameter of
the speculum is small in proportion to the length of the
instrument; it will bear a diameter of eight inches, with much
advantage for viewing very small stars, in consequence of the
great increase of the light.
The magnifying powers that are used are, forty, ninety, and two
hundred and fifty.”
Through the politeness of Prof. A. D. Bache, the committee were permitted
to compare the performance of Mr. Holcomb’s reflector with that of a
five feet achromatic, of four inches aperture, by Dolland, the property
of the University of Pennsylvania. The instrument was also compared with
a three and a half feet achromatic, by Dolland, and with a Gregorian of
four inches aperture, the mirrors of which had been lately repolished
in London. The short stay of Mr. Holcomb in Philadelphia, prevented the
comparison of it with reflectors in the possession of other members of
the committee.
On the evening of the 14th of April, the committee met by adjournment in
the open lot south of the Pennsylvania Hospital, the use of which was
politely permitted to the committee by the managers of that institution.