CHAPTER XXVI
THE SECRET TUNNEL IN THE MESA
At five o'clock Ned and Alan were astir. With regrets that they were not at Camp Eagle for a plunge in the cool mountain lake, they prepared another hot meal, ate it, and boarded the Cibola.
The balloon had now been inflated thirty-eight hours and was noticeably showing the loss of its gas. While the top of the bag was yet round and firm in the heat of the sun the lower sides had become a trifle flabby as the cool evening had come on. Up to this time all records for balloon flight had been broken a fact due to the renewed buoyancy caused each day by the hot, Southwestern Sun. And, exploration in and quick ascent from the canyons before them would before long call for the use of ballast. The boys agreed that the time had arrived to utilize their liquid hydrogen. The shrinkage that night had been quite perceptible.
They regretted that but two-thirds of this remained—about eleven cubic feet. This when reconverted meant nearly twelve thousand cubic feet of new gas at their present altitude. As the work of converting the gas involved care, preparation for it was made before the Cibola was cut loose.
The reconverter, a reduced inversion of the apparatus used in making liquid air, was made ready. When the muffled explosions and the heat of the tubes told the boys that the reconverter was working perfectly and pumping new and needed gas into the shrunken Cibola's long bag, the lashings were loosed and once more the faithful dirigible mounted skyward.
With Major Honeywell's map of the region spread out on the deck of the bridge and the binoculars in hand Ned began the long anticipated search for the lost city.
All day the process of turning the liquid hydrogen back into buoyant gas went on. And all day the Cibola wound her devious course over the peaks and chasms beneath. By night half the hydrogen jars were empty and Ned and Alan saw the evening close in on them without a sign of the object of their search. When darkness stopped further work the balloon was brought to earth and camp made again.
The following day, as uneventful as the first, gave no indication of the secret city. The rest of the liquid hydrogen was transformed into gas. The sun seemed to enfold the craft in a fiery embrace. When camp was made again that night the Cibola had been afloat eighty hours.