Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere (1875)
Lockyer, Norman, Sir, 1836-1920 · New York, D. Appleton and company · leaf 28
Mode of describing an Ellipse. The thread here represents the sum of the distances from each pointof the ellipse to the foci, and remains the same while the ellipse isdescribed. Draw an ellipse according to these directions. The Centre of an ellipse is the point midway betweenthe foci in the…
Astronomy
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