d 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 get the flash lamps ready, and when they
were all charged and they had eaten, they went back to the opening
to see if the air