HISTORY OF PHYSICAL ASTRONOMY.

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country, in consequence, enjoyed an exclusive privilege in the construc-tion of instruments of this description. At length Guinand, a humblemechanic of Brenetz, a small village in the Canton of Neufchatel, Swit-zerland , having turned his attention to the manufacture of Hint-glasstowards the close of the eighteenth century, succeeded, after a long courseof persevering efforts, in producing masses of that substance perfectly freeof striae, and therefore adapted for the construction of object-glasses oftelescopes. Frauenhofer *, the Bavarian optician, having been madeacquainted with the wonderful success of Guinand, resolved to take ad-vantage of the circumstance, and with a view to this object he inducedthe Swiss artizan to remove to Munich , in the year 1805. This eminentindividual, who was no less remarkable for sagacity in philosophicalenquiries than for skill as an artist, possessed peculiar qualifications forprofiting by the instructions of Guinand, and he soon succeeded in attain-ing unexampled excellence in the construction of achromatic object-glasses. Telescopes were now executed by Frauenhofer, the apertures ofwhich far exceeded anything hitherto known since the discovery of achro-matism. It was with one of these instruments, having an aperture of9.9 inches, and a focal length of 13 jj feet, that M. Struve made theseries of micrometrical measurements of double stars at Dorpat, betweenthe years 1824 and 1837, whieh have rendered the name of that astro-nomer so deservedly famous. With another of them, having an apertureof 12 inches, and a focal length of 18 feet, M. Lamont, of Munich ,made those interesting observations of the satellites of Uranus , to whichallusion has been made in one of the preceding chapters. Frauenhoferwas contemplating the execution of objeet-glasses of still greater mag-nitude than either of those above-mentioned, when his brilliant careerwas unfortunately brought to a close by a premature death. His succes-sors, MM. Merz and Mahler, have succeeded in effectually realising hisviews. Among the chef-d’ceuvres of these artists may be cited the famousrefractors of Pulkowa and Cambridge, U.S. , to both of which instru-ments allusion has already been made in the foregoing part of this work.

Guinand remained at Munich from 1805 till 1814, in which year hefinally returned to his native country. A few years afterwards he wasvisited by Lerebours, an eminent French optician, who purchased of himall the flint-glass in his possession. Subsequently he also supplied Can-choix, another artist of Paris , with portions of the same valuable substance.The French opticians skilfully worked the material into object-glasses,and in this manner refracting telescopes came to be constructed in France ,rivalling the most finished productions of the Munich artists. England,which continued long to be the exclusive seat of the manufacture ofachromatic telescopes, had the mortification of finally seeing both Ger-many and France completely outstrip her in this branch of practicaloptics. This result she owed to the short-sighted policy of the Govern-ment, which had placed an exorbitant duty on the manufacture of flint-glass. The removal of this pernicious impost a few years since, hasgiven a new impulse to the art, and already results have been achievedwhich seemed to indicate that before a long period shall have elapsed,refracting telescopes will be executed in this country, rivalling the most

* Joseph Frauenhofer was born in the year 1787, at Straubing, in Bavaria . Besideshaving attained unrivalled eminence in his professional vocation, he achieved manyimportant discoveries in physical optics. He died in 1826, while yet in the prime oflife; but he left behind him an immortal reputation.