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 18
hatfall upon it, and concentrates them in one spot, whichconsequently becomes hot and bright. If we merelyused a flat piece of glass the sunbeams would go THE KGONDAY GUN. 5 straight through; they would not be gathered together,and they would not be strong enough to burn the paper.The lens, you… … Fig. 3. — A Tell-tale for the Sun. are thus collected on the same spot, erich of them con-tributes a little warmth. Some ingenious person has turned this principle toan odd use, by arranging a burning-glass over a cannonin such a way that just when noon arrived the spot oflight should reach the…
Astronomy
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