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 28
of circular form, ° •**—> J *s>-> i *$>—> ! »» > J m~^>! >=*—-=► i Fig. 3. having their centre however not at P but at the gap inthe screen. This too I can readily illustrate to you inmy ripple-tank. The first of these two principles is really a conse-quence of the second,… … Fig. shape of the wave-front. Suppose (Fig. 4) we knewthat at a certain moment the wave-front of a set ofripples had got as faras the curved line FF,and that we wanted toknow where it wouldbe an instant later. Ifwe know how fast thewave travels we canthink of the time takento travel some shortspace…
Light · X-rays
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