Star-land; being talks with young people about the wonders of the heavens (1899)
Ball, Robert Stawell, Sir, 1840- [from old catalog] · Boston and London, Ginn & company · leaf 284
ons, and suchanother as the case of a body tossed straight up or THE USES OF THE PARABOLA. 271 dropped straight down, we may assert that the path ofa projectile is a parabola. There are some remarkable applications of the samecurve for practical purposes. From our lighthouses wewant to send beams… … Fig. 75.-— The Lighthouse Reflector. Much of it goes straight up into the air, much of itwould be directed inland; in fact, there is only anextremely small part of the entire number of rays thatwill naturally take the useful direction. We thereforerequire something round the lamp which shall…
Astronomy
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