Star-land : being talks with young people about the wonders of the heavens (1891)
Ball, Robert S. (Robert Stawell), Sir, 1840-1913 · London ; Paris : Cassell & Co. · leaf 20
the rays of light and heat, in sucha way that they are all directed into one point, which we The Sun. 5 call the focus. When a great number of rays are thuscollected on the same spot, each of them contributes alittle warmth. And just as a penny a day put into amoney-box makes more than thirty… … Fig. 3.—A Tell-tale for the Sun. odd use, by arranging a burning-glass over a cannon in sucha way, that just when noon arrived, the spot of light shouldreach the touch-hole of the cannon and fire it off. Thusthe sun itself is made to announce the middle of the day.(Fig- 2.) Another application of…
Astronomy
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