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 53
cave in shape,and therefore will march to a focus. What sort of apiece of glass will do this ? A mere window-pane willnot. A thick slab will not, seeing it is equally thick allover. Clearly it must be a piece of glass that is thickerat one part than another. Well, suppose we take apiece of glass… … and bulging on the other face. Think of the time whena wave-front has arrived at GO. A moment later wherewill it be ? The middle part that strikes at M will be goingthrough glass to B. This distance MB we know will beonly two-thirds as great as the distance to which it wouldgo -in air. Had it gone…
Light · X-rays
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