ful success of Guinaud, and induced the Swiss mechanic to
leave Brenetz and enter into partnership with him at Munich in 1805.

The result was perfectly successful; and the new firm turned out some
of the largest object-glasses which had until then been made. 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. The
former belongs to Mr. Newall, a gentleman who, connected with those who
were among the first to recognise the genius of our great English
optician, Cooke, did not hesitate to risk thousands of pounds in one
great experiment, the success of which will have a most important
bearing upon the astronomy of the future."[7]

The progress which Mr. Cooke made in his enterprise was slow but
steady. Shortly after he began business as an optician, he became
dissatisfied with the method of hand-polishing, and made arrangements
to polish the object-glasses by machinery worked by steam power. By
this means he secured perfect accuracy of figure. He was also able to
turn out a large quantity of glasses, so as to furnish astronomers in
all parts of the world with telescopes of admirable defining power, at
a comparatively moderate price. In all his works he endeavoured to
introduce simplicity. He left his mark on nearly every astronomical
instrument. He found the equatorial comparatively clumsy; he left it
nearly perfect. His beautiful "dividing machine," for marking
divisions on the circles, four feet in diameter and altogether
self-acting--which divides to five minutes and reads off to five
seconds is not the least of his triumphs.

The following are some of his more important achromatic te