taught artist should "beat the most skilful opticians of Europe.
The telescopes of Mr Clarke have been brought under the notice of English astronomers, chiefly through the Rev. Mr Dawes, one of our most reliable observers. He has made some important astronomical discoveries; and perhaps there is not a better judge of the performance of telescopes. The readers of the Notices of the Astronomical Society are familiar with the achievements of Mr Clarke's telescope in the hands of Mr Dawes. Admiral Smyth, another of our most laborious astronomers, bears ample testimony to the perfection in his art, acquired by the American optician. We have, then, good ground for hoping that this great telescope will mark another decided advance in astronomical discovery.
It may, at first sight, appear strange, that the object-glass of a refracting telescope cannot be made of great dimensions with as great facility as the metallic speculum of a reflecting telescope. The speculum of Lord Rosse's telescope is six feet in diameter; and yet this lens of Mr Clarke, though only eighteen inches, is regarded as one of monster dimensions. Apart from the working of the figure, there is this great difference, that, for the glass to perform well, it must be perfectly homogeneous throughout; while this is of no importance in the reflecting telescope. In the one case, the rays have to pass through the substance of the glass, and any
