Imperial Privileged National Gazette

parents and brothers, the latter will remain unrevealed, and even in the event that he should have already taken up another trade by his own estimation, he will not be reclaimed, but rather should receive certain support for the time being through this.

With the first news from him, he is also free to provide an address through which one can safely let letters reach him, just to be able to show his hand to the distressed parents as proof of his life and well-being for the time being; afterwards, however, the closer circumstances would be necessary to know, which he could possibly enclose with the letter on a special sheet.

Should he find himself in the military: then all gentlemen regiment chiefs, for whom it is a joy to dry the tears of troubled parents, are also urgently asked to let his residence and situation be discovered through their subordinates under the above address, and to be assured of the heartiest thanks along with reimbursement of expenses.

Gotha, end of November 1794.

Arts, Manufactures, and Factories.

Answer to the inquiry in the R. A. Reichs-Anzeiger 1794. 2nd Vol. Num. 142. p. 1348. regarding the manufacture of achromatic telescopes. *)

The English artists certainly have neither a special calculation nor special tricks regarding these telescopes, for the theory of them is now so perfect that nothing more is to be expected on this subject, and thus no secret can exist. See Klügel’s Dioptrics p. 105, 125, 161, also Foot’s guide on how all types of telescopes are to be manufactured in the greatest possible perfection, translated by Klügel, where, for example, it is shown how one can obtain a 320-fold magnification in the

diameter through a five-inch telescope, for which one formerly would have needed a 200-foot, but nearly unusable telescope. In these books, therefore, the sender of this question finds specific theoretical answers to all his questions. But as far as the practical determination of the required lens sheets is concerned, it goes here as with all applications of theory: it indeed gives general guidance, and protects against detours and errors, but since it presupposes things which cannot be precisely stated in practice, it often leaves one in the lurch where one needs it most; and precisely the fine and exact calculation of the refraction and dispersion ratio, the thickness, and focal length of those two types of glass, which Mr. Suß admires in the Eulerian theory, makes the application of the theory impossible in such precision. For who wants to state the size of these elements in such small parts as the theory requires, safely? The suspicion of the questioner, that English artists arrange several glasses together until they turn out according to their purpose, is therefore not very likely, but is also actually founded according to certain reports: See Gehler’s Physical Dictionary, Article: achromatic telescopes and flint glass.

If German artists now do not deliver such work as English ones, the fault likely lies solely with the prejudice of the Germans for everything that comes from England, and with the poor support of German artists. Incidentally, it is unfounded that German artists deliver nothing similar, as the gentleman sender of the question believes. Tiedemann in Stuttgart has been manufacturing achromatic telescopes for many years that yield nothing to the English in perfection, even if they are 8 times cheaper. Proofs of this assertion are the testimonies of a Sachs and other competent judges, which he can present.

*) In Num. 152. p. 1449. 2nd Vol. 94. there is indeed already an answer to that inquiry from a man who has such a decisive judgment on the touched subject as a competent judge that it likely needs no further confirmation; nevertheless, this answer also deserves a place here, especially because of the special information contained therein about Tiedemann's, this great German artist's, achromatic telescopes.