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 had cleared.  Tom tested it by dropping a match down, and, to his delight it burned with a clear flame.

“It’s all right!” he exclaimed.  “The air is pure.  Now to see where we will bring up.  Come on, everybody.”

“Jest one minute, Massa Tom,” begged Eradicate, as the young inventor was about to descend the steps, which even the brightness of his lamp did not disclose the end.  “Is yo’ gwine down dar, Massa Tom?”

“Certainly, Rad.”

“An’ is yo’—­’scuse me—­but is yo’ expectin’ me fo’ t’ follow yo’?”

“Certainly, Rad.”

“Den, all I’s got t’ say is dat yo’ is ‘spectin’ too much.  I ain’t gwine t’ bury mahse’f alive not yit.”

“But, Rad, this is where the gold images are.  If you don’t come down with us you won’t get any gold.”

“Am dat so?  No gold?” The colored man scratched his head.  “Well, I shore does want gold,” he murmured.  “I reckon I’d better trot along.  But one thing mo’, Massa Tom.”

“What is it, Rad?”

“Was yo’ all aimin’ t’ stay down thar any length ob time?  ’Case if yo’ is yo’ all’d better take along a snack ob suffin’ t’ eat.  ’Case when I gits among gold I don’t want t’ come out very soon, an’ we might stay dar all day.”

“Good advice, Rad,” exclaimed Ned with a laugh.  “I think we may get hungry.  You go back and put us up a lunch.  We’ll wait for you.”

“Bless my napkin ring!  I think you’re right!” exclaimed Mr. Damon, and Eradicate hurried back to the balloon to get some of the condensed food.

He was soon back and then, with Tom in the lead, and with everyone carrying an electric torch, with a spare one in reserve, and with their weapons in readiness the party descended the stone steps.

Their footfalls echoed solemnly as they went down—­down into the unknown blackness.  They kept their bright lights playing here and there, but even these did not dispell the gloom.  On every side was stone—­stone walls—­stone steps.  It was like going down into some vast stretch of catacombs.

“Say, will we ever get to the bottom?” asked Ned, when they had counted several hundred steps.  “Maybe this goes down to the middle of the earth.”