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 44
amp, my assistant causes a broad beam of light tostream forth. The air is dusty, and each little particleof dust catches a portion of the beam, and helps youto see which way it is marching. In this beam I hold a LIGHTS AND SHADOWS 27 concave silvered mirror. At once you see how by print-ing a… … Fig. 15. focus, and concentrate the waves in different places atwill. If I replace the concave mirror by a convex one, Ishall cause a divergence of the waves. No longer isthere any real focus, but the waves now inarch awayas if they had come from a virtual focus behind themirror at F (Fig. 16),…
Light · X-rays
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