"What's the matter?" asked Kemp, when the Invisible Man admitted him.

"Nothing," was the answer.

"But, confound it! The smash?"

"Fit of temper," said the Invisible Man. "Forgot this arm; and it's sore."

"You're rather liable to that sort of thing."

"I am."

Kemp walked across the room and picked up the fragments of broken glass. "All the facts are out about you," said Kemp, standing up with the glass in his hand; "all that happened in Iping, and down the hill. The world has become aware of its invisible citizen. But no one knows you are here."

The Invisible Man swore.

"The secret's out. I gather it was a secret. I don't know what your plans are, but of course I'm anxious to help you."

The Invisible Man sat down on the bed.

"There's breakfast upstairs," said Kemp, speaking as easily as possible, and he was delighted to find his strange guest rose willingly. Kemp led the way up the narrow staircase to the belvedere.

"Before we can do anything else," said Kemp, "I must understand a little more about this invisibility of yours." He had sat down, after one nervous glance out of the window, with the air of a man who has talking to do. His doubts of the sanity of the entire business flashed and vanished again as he looked across to where Griffin sat at the breakfast-table--a headless, handless dressing-gown, wiping unseen lips on a miraculously held serviette.

"It's simple enough--and credible enough," said Griffin, putting the serviette aside and leaning the invisible head on an invisible hand.

"No doubt, to you, but--" Kemp laughed.

"Well, yes; to me it seemed wonderful at first, no doubt. But now, great God! ... But we will do great things yet! I came on the stuff first at Chesilstowe."

"Chesilstowe?"

"I went there after I left London. You know I dropped medicine and took up physics? No; well, I did. _Light_ fascinated me."

"Ah!"

"Optical density! The whole subject is a network of riddles--a network with solutions glimmering elusively through. And being but two-and-twenty and full of enthusiasm, I said, 'I will devote my life to this. This is worth while.' You know what fools we are at two-and-twenty?"

"Fools then or fools now," said Kemp.

"As though knowing could be any satisfaction to a man!

"But I went to work--like a slave. 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."

"Precisely," said Griffin. "But consider, visibility depends on the action of the visible bodies on light. Either a body absorbs light, or it reflects or refracts it, or does all these things. If it neither reflects nor refracts nor absorbs light, it cannot of itself be visible. You see an opaque red box, for instance, because the colour absorbs some of the light and reflects the rest, all the red part of the light, to you. If it did not absorb any particular part of the light, but reflected it all, then it would be a shining white box. Silver! A diamond box would neither absorb much of the light nor reflect much from the general surface, but just here and there where the surfaces were favourable the light would be reflected and refracted, so that you would get a brilliant appearance of flashing reflections and translucencies--a sort of skeleton of light. A glass box would not be so brilliant, not so clearly visible, as a diamond box, because there would be less refraction and reflection. See that? From certain points of view you would see quite clearly through it. Some kinds of glass would be more visible than others, a box of flint glass would be brighter than a box of ordinary window glass. A box of very thin common glass would be hard to see in a bad light, because it would absorb hardly any light and refract and reflect very little. And if you put a sheet of common white glass in water, still more if you put it in some denser liquid than water, it would vanish almost altogether, because light passing from water to glass is only slightly refracted or reflected or indeed affected in any way. It is almost as invisible as a jet of coal gas or hydrogen is in air. And for precisely the same reason!"

"Yes," said Kemp, "that is pretty plain sailing."

"And here is another ............