Chapter XIX. The Underground River

They gathered around the opening so unexpectedly disclosed to them, and stared down into the black depths. Beyond the first few steps of the flight that led to they knew not where, nothing could be seen. In his impatience Tom was about to go down.

"Bless my match box!" cried Mr. Damon. "What are you going to do, Tom, my boy?"

"Go down there, of course! What else? I want to get to the underground city."

"Don't!" quickly advised the odd man. "You don't know what's there. It may be a trap, where the old Aztecs used to throw their victims. There may be worse things than bats there. You'll need torches-- lights--and you'd better wait until the air clears. It may have been centuries since that place was opened."

"I believe that's right," agreed Ned. "Whew; Smell it! It's as musty as time!"

An unpleasant odor came up the tunnel entrance, and it was stifling to stand too close. Tom lighted a match and threw it down. Almost instantly the flame was snuffed out.

"We couldn't live down there a minute," said the young inventor. "We've got to wait for it to clear. We'll go back to the balloon and get some electric flash lamps. I brought along a lot of 'em, with extra strong batteries. I thought we'd need some if we did find the city of gold, and it looks as if we were almost there now."

Tom's plan was voted good so they hurried out of the temple, their feet echoing and re-echoing over the stone floor. The place, ruined and desolate as it was, had no terrors for them now. In fact they were glad of the very loneliness, and Tom and Ned actually looked about apprehensively as they emerged, fearing they might see a sign of the Mexicans or the Fogers.

"Guess they can't pick up our trail," said Tom, when, he saw of what Ned was thinking.

"No, we've got the place to ourselves. I wonder how long it will take for the air to get fresh?"

"Not so very long, I guess. There was a good draught. There must be some opening in the underground city by which the air is sucked in. They'd never have only one opening to it. But we don't need to look for the other. Come on, we'll get out the torches."

These electrical contrivances are familiar to all boys. A small electric lamp is set in the end of a hollow tube of tin, and about the lamp is a reflector. Dry electrical batteries are put in the tin tube, and by means of a push button the circuit is closed, illuminating the lamp, which gives a brilliant glow. Tom had a special kind of lamp, with tungsten filaments, which gave a very powerful light, and with batteries designed to last a long time. A clip on the spring controlling the push button made it so that the lamp could be made to give a steady glow. Thus they were well prepared for exploring the tunnel.

It took some little time to