Johnson, George Lindsay, 1854- · New York, E. P. Dutton and Co. · leaf 25
will at once form a fresh centre of disturbance and will generate a new sphere, and this again another, and so on. Now every one of these tiny spheres may be supposed to lie side by side, each overlapping its fellow, forming tangents to points on their combined circumference, which points are… … (Fig. 1) may thus be considered as the crest of a wave, and the space between it and the next wave front (A^, A^) as the trough of a wave. Thus light waves advance to form an ever enlarging sphere, and the tangent to this sphere represents the wave front. Since the centre of each tiny sphere lies…
Color photography
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.
