A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope.
Read more about Primary Mirror: Description, Superlative Primary Mirrors
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“But the doctrine of the Farm is merely this, that every man ought to stand in primary relations to the work of the world, ought to do it himself, and not to suffer the accident of his having a purse in his pocket, or his having been bred to some dishonorable and injurious craft, to sever him from those duties.”
—Ralph Waldo Emerson (1803–1882)
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—Mme. Ellen Louise Demorest 1824–1898, U.S. women’s magazine editor and woman’s club movement pioneer. Demorest’s Illustrated Monthly and Mirror of Fashions, p. 203 (January 1870)