April 26. 58 | Observatory | Armagh
Dear Sir
In the Astron Nachrichten No 1138 is a paper2 by Steinheil3 on Specula of Silvered Glass which I think may be worth inserting in the Phil Magazine.4 As to his claim of priority over Foucault,5 I cannot offer an opinion, as I have no access to the Algemeine Zeitung.6 Some years since he proposed a very crude plan, the deposition of Silver of Gold by the Electrotype on polished mould.
The photometric results agree closely with those obtained by Mr Grubb7 and myself, and show clearly that a Reflecting telescope with specula of silver, may have more light than a good achromatic of equal aperture.
He seems however to have contemplated only a spherical figure for the concave speculum, and proposes to correct it by a small achromatic which is over corrected. This would lose light and introduce complicated adjustment; and he seems not to be aware that the parabolic figure can be given to glass as well as speculum metal. I think also that the plans which he proposes for improving meridian and Equatorial instruments will be found impracticable from the very great difficulty of forming the large plane specula which they require.
Believe me | yours ever | T.R. Robinson
Dr Tyndall
RI MS JT/1/R/32
RI MS JT/1/TYP/3/1019
Thomas Romney Robinson: see letter 1501, n. 1.
a paper: see Steinheil, Dr., ‘On the Advantages to be derived from the Use of Silver Mirrors for Reflecting Telescopes, and on a Novel Method of Mounting such Instruments (Translation of a letter from C.A. Steinheil of Munich, to Professor C.A.F. Peters of Altona, published in No. 1138 of the Astronomische Nachrichten)’, Monthly Notices of the Royal Astronomical Society, 19 (1858), pp. 56–60.
Steinheil: Karl August Steinheil (1801–70), a German physicist and astronomer who was professor of mathematics and physics at the University of Munich, 1832–70. In 1854 he opened an optical workshop in Munich that became renowned for its instruments and telescopes for astronomy and telegraphy (CDSB).
which I think may be worth inserting in the Phil Magazine: Steinheil’s paper was not published in the Phil. Mag.
Foucault: Jean Bernard Léon Foucault (1819–68), a French physicist known for the invention of the Foucault pendulum, an instrument he used to prove the rotation of the Earth in 1851. Tyndall translated and abridged Foucault’s work for the Phil. Mag. (CDSB).
Algemeine Zeitung: a daily political journal in Germany, founded in 1798.
Mr Grubb: Thomas Grubb (1800–78), an Irish optical engineer (CDSB).
Please cite as “Tyndall1514,” in Ɛpsilon: The John Tyndall Collection accessed on