At the Great Exhibition of London, in 1862, two large circular blocks of glass, about two inches thick and twenty-six inches in diameter, were shown by the manufacturers, Messrs.
Chance of Birmingham.

These discs were found to be of perfect quality, and suitable for object-glasses of the best kind.

At the close of the Exhibition, they were purchased by Mr.Newall, and transferred to the workshops of Messrs.

Cooke and Sons at York.

To grind and polish and mount these discs was found a work of great labour and difficulty.