Note 1 — CONCLUSION.
Reading edition
"In this series of light rays it is plain that there are two gaps, or unknown regions, regarding which we have to confess total ignorance relative to the part they play in the economy of the universe. May there not exist vibrations still more rapid? That question we are not permitted to answer. Be that as it may, the invisible rays are incomparably more numerous than the visible ones. Our eyes thus see almost nothing of that which exists. Our assumed knowledge is only an insignificant islet in the midst of the ocean of the infinite."—Sir William Crookes.