When the hole was looked at from a moderate distance through a narrow slit (about 1/30 inch wide) interposed between the eye and the lens, there was seen only a single row of circular spots, which were arranged sinuously, as shown in Fig. 22. A slight movement of the slit in the direction perpendicular to its length produced a wave-like motion of the circles, suggestive, as pointed out by the excellent observer before referred to of the wriggling of a caterpillar. [Illustration: _Fig. 22.--Multiple Images seen through a Slit._] By sufficiently increasing the distance between the source of light and the eye, as many as twenty-four or twenty-five bright spots might be made to appear in the row, but they could not be counted with any great certainty. At a still longer distance or with a lens of shorter focus (convex or concave) they became less distinct, and finally seemed to be resolved into a multitude of small blurred images--probably several hundreds--which were separated from one another by hazy dark lines. [Illustration: _Fig. 23.--Images of an electric lamp Filament._] I thought that the observations might be rendered easier if the source of light had a more distinctive and conspicuous form than that of a simple circle. Some experiments were therefore made with semi-circular and triangular holes, and these were in some respects preferable; but far better results were afterwards obtained by using as a source of light the horse-shoe shaped filament of an electric lamp, screened by a coloured glass. When such a lamp was looked at through a lens, concave or convex, of about six inches focus, from a distance of a few feet, the roughly oval patch of luminosity formed upon the retina, instead of being a mere ill-defined blur, such as would be produced if the transparent media of the eye were composed of homogeneous substances like glass or water, appeared to be made up of a crowd of separate images of the filament, some being brighter than others, as is shown in the diagram Fig. 23. [Illustration: _Fig. 24A.--Images with horizontal Slit._] [Illustration: _Fig. 24B.--Images with vertical Slit._]