"Right you are!" cried the balloonist. The car was scarcely stopped when he had leaped out, and had the lifting jack under the left rear wheel, where the tire had gone to the bad. He and Tom labored like Trojans to take off the wheel, and put on the other. They lost five minutes, and when they got under way again the red and the green cars were three quarters of a lap ahead. "You've got to catch them!" declared Sharp firmly. But the red and the green car drivers saw their advantage, and were determined to hold it. Tom could not catch them without going his limit, and he did not want to do this just yet. However, he had his opportunity when about two hundred miles had been covered. Both the red and the green cars had tire troubles, but the red one was delayed scarcely two minutes as there was a corps of mechanics on hand to take off the defective wheel and put on another. Still Tom regained his lost ground, and once more the race between those three cars was even. In the rear of Tom's car Mr. Sharp was mending the blown-out tire, though there was still one spare wheel on reserve. Tom, in front, peered eagerly at the track. Nearly side by side raced the red and the green cars, the latter somewhat to the rear. It was at the three hundred and fiftieth mile that Tom had another blow-out. This time it took a little longer to change the wheel, and the red and green cars gained a full lap on him. The track was now so dusty that it was difficult to see the contesting cars. Many had dropped out, and more were on the verge of giving up. With the odds against him, Tom started in to regain the lost ground. Narrowly he watched his electric power. Slowly he saw it dropping. Would he have enough left to finish out the race? He feared not. The hours were passing. Still there was a hundred miles yet to go twenty circuits of the track. Some of the spectators were getting weary and leaving. The band played spasmodically. Suddenly Tom saw the red car shoot to one side of the track, toward a charging station; The green car followed. "That's our cue!" cried the young inventor "We need a little more 'juice' and now is the time to get it." The lad ran to the shed where his charging wires were, and they were connected in a trice. He allowed twenty-five minutes for the charging, as he knew with his improved battery he could get enough current in that time to finish the contest. Before the red and green car drivers had finished installing new batteries, for they could not recharge as quickly as could our hero, Tom was on the track again. But, in a little while, his two rivals were after him. It was now a spectacular race. Around and around swept the three big cars. All the others were practically out of it. The crowd became lively airs. Mile after mile was reeled off. The day was passing. Tired and covered with dust from the track, Tom still sat at the steering wheel.