I know of a gentleman who made a hundred of these specula with his own hands.
For they had not only to design and make the specula, but also the mountings of the mirrors as well.
In the construction of reflecting telescopes, concave mirrors, or specula, are combined with a double convex lens.
The specula are made of speculum metal, which is a composition of certain proportions of copper and tin.
I do not know whether before that the Abb Rochon had thought of using the metal Platina for the specula telescope.
His writings on light, Perspectiva and Specula mathematica, are included in his Opus majus.
It also admits of as perfect a polish as the metal hitherto used for the specula of telescopes.
He studied science when he could, and hired a telescope, until he learnt to make his own specula and telescopes.
The Specula Melitensis Encyclica gives an account of a kind of calculating machine of his invention.
This artifice of a double melting is often had recourse to, and especially in casting the alloys for the specula of telescopes.