to pursue his investigations with entire safety. Accordingly he
grew venturesome, and began to go out-of-doors at all hours of the day
or night. And then on the fourteenth day after his arrival in the city
his immunity came abruptly to an end.

It was early in the forenoon, and Constans was exploring a quarter of
the city that lay to the northeast of the Citadel Square. He became
interested in the curious, bridgelike structure which spanned the
street; enough of it remained standing to show him that it had been
designed for overhead traffic, a highway in the air. There were the
rails, the signal-boxes, and other mysterious adjuncts of the ancient
railways; he had read about them in his books and he recognized them at
once.

Now this particular section of the aerial railway must have been a
branch line, for it ended abruptly in front of a building of unusual
size and consequent importance. Beyond this again could be seen a
surface net-work of iron rails converging to the black mouth of a great
tunnel--a highway under the earth. Constans felt a lively impulse to
push his explorations further. This was evidently a terminal station of
the wonderful steel roads of the ancients; within the building itself he
might reasonably expect to find some of the old-time engines and wagons
with which the traffic had been carried on.

Passing through a central hall of fine proportions, Constans found
himself standing under an immense arched structure of stone and iron and
glass. The ancient car-shed, so Constans conjectured; then he paused
excitedly before a long platform, at which stood a complete train, made
up and ready to start.

Constans examined this new find with critical attention. The enormous
locomotive-engine, with its driving-wheels that stood higher than a
man's head, impressed him mightily, for all that the monster's burning
heart had grown cold and its stentor breathing had been hushed forever.
He climbed into the cab and wondered hugely at the multiplicity of
stopcocks and levers and cabalistically lettered dials. It seemed
incredible that the giant could have moved even his own weight, and yet
there was his appointed task strung out behind him, fifteen long and
heavy vehicles--it was amazing!

Behind the engine came the cars for luggage, piled high with bags and
boxes, and then the regular train equipment, a long line of coaches.
These last were of the most luxurious pattern--that was plain to see,
although the va