Light visible and invisible : a series of lectures delivered at the Royal Institution of Great Britain, at Christmas, 1896 (1897)
Thompson, Silvanus Phillips, 1851-1916, Royal Institution of Great Britain · New York : Macmillan · leaf 227
red-hot iron ballis slung by a hook in the focusof the mirror, and it is hoistedup again into its position abovethe table. The ball being atthe focus, the mirror collectsthe diverging waves and reflectsthem straight down in a parallelbeam. It is a beam of invisibleinfra-red waves, accompaniedby a… … Fig. 11- v THE INVISIBLE SPECTRUM 207 intolerably hot. I hold in the focus a bit of blackpaper, at once it smokes, and kindles into visible com-bustion. Other things can be lighted. Here is acigar. Holding it in the focus it absorbs enough wavesto warm it up; and the ascending wreath of smokeproves…
Light · X-rays
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