With one of these instruments, having an aperture of 9.9 inches, Struve, the Russian astronomer, made some of his greatest discoveries.

Frauenhofer was succeeded by Merz and Mahler, who carried out his views, and turned out the famous refractors of Pulkowa Observatory in Russia, and of Harvard University in the United States.

These last two telescopes contained object-glasses of fifteen inches aperture.
The pernicious impost upon flint glass having at length been removed by the English Government, an opportunity was afforded to our native opticians to recover the supremacy which they had so long lost.

It is to Thomas Cooke, more than to any other person, that we owe the recovery of this manufacture.

Mr.Lockyer, writing in 1878, says: "The two largest and most perfectly mounted refractors on the German form at present in existence are those at Gateshead and Washington, U.S.