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 40
in which a shadow is cast by it. If I set up LIGHTS AND SHADOWS 2.3 (Fig. 12) this little dagger on a whitened board I cansee which way its shadow falls. If now I place a candlebeside it on the board at P it casts a shadow of thedagger on the side away from P. Next, set up a pieceof silvered mirror… … Fig. 12. you see by the direction in wrhich this second shadowfalls that it falls just as if the light had come from asecond candle placed at Q, just as far behind the mirroras P is in front. Let us put an actual second candle atQ, and then take away the mirror, and you see thesecond shadow in the…
Light · X-rays
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