Philosophical instructor, or, Webster's elements of natural philosophy : subdivided into principles and illustrations ; intended for academies, medical schools, and the popular class-room (1824)
Eaton, Amos, 1776-1842, Webster, John, fl. 1804-1824 · Albany : Printed by Websters and Skinners ... · leaf 177
cting telescopes are those which are chieflyformed by mirrors, and reflect the object to the eye,instead of refracting. They are principally confinedto two kinds, called the Gregorian and Newtonian. In the construction of the Newtonian, let a b c d bea large tube, open at the end c d, and closed at… … FB tant object, being considered as parallel to each other,fall on the concave speculum e f, and are reflectedback upon a small plane speculum l, which is in-clined in an angle of 45° ; from this mirror they areagain reflected to a convex lens, which is fixed in theside of the tube, and converged…
Physics
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