Several days before, when Matt had been planning to start for Denver on his motor-cycle, he had bought an auxiliary gasoline-tank. The tank that came with the machine was attached behind the saddle, and held five quarts, sufficient for a run of 75 to 100 miles. The auxiliary tank was attached to the top tube, and its tubes and connections were so arranged that it could be used independently of the tank behind. With both tanks filled, the Comet's radius of action was increased at least 75 miles—enough to carry the machine half-again as far as Prescott.
Matt had never experienced any trouble with the Comet. As a rule, common sense and ordinary thoughtfulness are enough to keep any good motor-cycle on the road without repair bills. The Comet was always as spick and span as when it came from the factory, for Matt groomed the machine as he would have groomed a race-horse, and cleanliness is one of the first points to look after if a machine is to travel right. On his return from a trip he never failed to go over the motor-cycle with wrench and pliers, to inject a few squirts of kerosene into the warm cylinders, and to "turn over" the engine a few times. He was busy making a final survey of the Comet when Chub pounded up on Clip's machine. A canteen, lashed to the head of the one-cylinder, showed that Chub had been thoughtful enough to secure a reserve supply of gasoline.
"All ready?" sang out Matt.
"Ready's whole family," answered Chub.
Two minutes later the boys were skimming north along the Cave Creek road. Beyond the outlying canal they struck the hills, and here Matt instructed Chub a little in nursing his machine—not to open the muffler when there was no real necessity, to let the burned oil out of the motor base at least once every fifty miles, and to cut off the power when descending hills in order to cool and help the engine.
They were well into the hills before Matt told Chub about the second letter, and showed it to him.
"Thunder!" exclaimed Chub. "It must be a swift bunch we're up against. But I guess they're four-flushin'. Anyhow," he grinned, "I'm not scared so you can notice it."
"It makes me think," said Matt, "that there's something in that first note, in spite of Short's opinion."
"Sure," answered Chub. "That first note is lookin' better and better to me. Different fists worked on those two letters. The last one must have been jotted down by a fellow who'd been through the eighth grade, anyhow. How do you size 'em up?"
"It's all guesswork, Chub, but my guess is that some party intends giving us a tip, and that another one found it out, and is trying to backcap the first man. The tip must be important, or the second man wouldn't try to keep us away from Prescott. To follow the thing farther, the second man may be one of the two who held up Fresnay."