noun, plural spec·u·la [spek-yuh-luh] /ˈspɛk yə lə/, spec·u·lums.
Origin of speculum
Examples from the Web for specula
It also admits of as perfect a polish as the metal hitherto used for the specula of telescopes.
I know of a gentleman who made a hundred of these specula with his own hands.The Vast Abyss|George Manville Fenn
The Specula Melitensis Encyclica gives an account of a kind of calculating machine of his invention.
He studied science when he could, and hired a telescope, until he learnt to make his own specula and telescopes.History of Astronomy|George Forbes
His writings on light, Perspectiva and Specula mathematica, are included in his Opus majus.