“But I went to work⁠—like a nigger. And I had hardly worked and thought about the matter six months before light came through one of the meshes suddenly⁠—blindingly! I found a general principle of pigments and refraction⁠—a formula, a geometrical expression involving four dimensions. Fools, common men, even common mathematicians, do not know anything of what some general expression may mean to the student of molecular physics. In the books⁠—the books that tramp has hidden⁠—there are marvels, miracles! But this was not a method, it was an idea, that might lead to a method by which it would be possible, without changing any other property of matter⁠—except, in some instances colours⁠—to lower the refractive index of a substance, solid or liquid, to that of air⁠—so far as all practical purposes are concerned.”

“Phew!” said Kemp. “That’s odd! But still I don’t see quite⁠ ⁠… I can understand that thereby you could spoil a valuable stone, but personal invisibility is a far cry.”