What does Marvel tell himself in regard to the incident? How is he convinced otherwise?

"Am I drunk?" said Mr. Marvel. "Have I had visions? Was I talking to myself? What the—"

"Peewit, indeed!" said Mr. Thomas Marvel. "This ain't no time for foolery." The down was desolate, east and west, north and south; the road with its shallow ditches and white bordering stakes, ran smooth and empty north and south, and, save for that peewit, the blue sky was empty too. "So help me," said Mr. Thomas Marvel, shuffling his coat on to his shoulders again. "It's the drink! I might ha' known."

"Oh, come! I ain't blind. You'll be telling me next you're just thin air. I'm not one of your ignorant tramps—"

Marvel is convinced when the invisible man actually touches him.

"Let's have a hand of you," said Marvel, "if you are real. It won't be so darn out-of-the-way like, then—Lord!" he said, "how you made me jump!—gripping me like that!"

He felt the hand that had closed round his wrist with his disengaged fingers, and his fingers went timorously up the arm, patted a muscular chest, and explored a bearded face. Marvel's face was astonishment.

"I'm dashed!" he said. "If this don't beat cock-fighting! Most remarkable!—And there I can see a rabbit clean through you, 'arf a mile away! Not a bit of you visible—except—"