"Write something — with your pen, I mean," said Inwood.
Simon took out his fountain-pen and scribbled a couple of words on the back of the menu. Inwood blew on it till it dried, and handed it back.
"Now rub it over with that crayon."
Simon did so, and the writing disappeared. It vanished quite smoothly and easily, at a couple of touches, without any hard rubbing, and the paper was left without a trace of discoloration or roughness.
"Just a useful thing for banks and offices," said Inwood.
"There's nothing else like it. An ink eraser tears up the paper. You can buy a chemical bleacher, and several firms use it, but that's liquid — two re-agents in separate bottles, and you have to put on drops of first one and then the other. That thing of mine is twice as simple and three times quicker."
Simon nodded.
"You're not likely to make a million out of it, but it ought to have quite a reasonable sale."
"I know that," said Inwood bitterly. "I didn't want a million. I'd have been glad to get a thousand. I've told you — I'm not such a genius as I thought I was. But a thousand pounds would have put us on our feet again — given me a chance to open a little shop or find a steady job or something. But I'm not going to get a penny out of it. It isn't my property — and I invented it!.. We've been living on capital as well as income. This would have put us straight. It had to be protected."
The old man's faded eyes blinked at the Saint pitifully. "I don't know anything about things like that. I saw a patent agent's advertisement in a cheap paper, and I took it to him. I gave him all my formulae — everything. That was a fortnight ago. He told me he'd have to make a search of the records before my patent could be taken out. I had a letter from him this morning, and he said that a similar specification had been filed three days ago."