“If the trial succeeds,” Overholt said, still instinctively seeking to forestall a disappointment he did not expect.  “Nothing is a fact until it has happened, you know!”

“Well,” said Newton, “if I had anything to bet with, and somebody to bet against, I’d bet, that’s all.  But I haven’t.  It’s a pity too, now that everything’s coming out right.  Do you remember how we were trying to make bricks without straw less than a month ago, father?  It didn’t look just then as if we were going to have a roaring old Christmas this year, did it?”

He chattered on happily, looking at the Motor all the time, and Overholt tried to smile and answered him with a word or two now and then, though he was becoming more and more nervous as the minutes passed and the supreme moment came nearer.  In his own mind he was going over the simple operations he had to perform to start the engine; yet easy as they were he was afraid that he might make some fatal mistake.  He did not let himself think of failure; he did not dare to wonder how he should tell his wife if anything went wrong and all her hard-saved earnings were lost in the general ruin that must follow if the thing would not move.  There was next to nothing left of what she had sent, now that everything was paid for; it would support him and the boy for a month, if so long, but certainly no more.

He was ready at last, but, strange to say, he would gladly have put off the great moment for half an hour now that there was no reason for waiting another moment.  He sat down again in his chair and folded his hands.

“Aren’t you going to begin, father?” asked Newton.  “What are you waiting for?”

Overholt pulled himself together, rose with a pale face, and laid his shaking hands on the heavy plate-glass case.  It moved upwards by its chain and counterpoise, almost at a touch, till it was near the low ceiling, quite clear of the machine.

He was very slow in doing what was still necessary, and the boy watched him in breathless suspense, for he had seen other trials that had failed—­more than two or three, perhaps half a dozen.  Every one who has lived with an inventor, even a boy, has learned to expect disappointment as inevitable; only the seeker himself is confident up to a certain point, and then his own hand trembles, when the moment of trial is come.

Overholt poured the chemical into the chamber at the base, screwed down the air-tight plug, and opened the communication between the reservoir and the machine.  Then he took out his watch and waited four minutes, that being twice the time he had ascertained to be necessary for a sufficient quantity of the liquid to penetrate into the distributors beyond.  He next worked the hand air-pump, keeping his eye on the vacuum gauge, and lastly, as soon as the needle marked the greatest exhaustion he knew to be obtainable, he moved the starting lever to the proper position, and then stepped back to watch the result.