pulled down, and instantly the jarring and clanking gave way to a
decided rumble, low and distinct, but so powerful that it shook the
air. At the same time the agent quit his post and went over to the
giant horizontal cylinder.

Now Smith could see that this vast structure was merely part of an
engine whose dimensions were quite beyond any former experience. It
was a simple affair, being merely a reciprocal machine like the most
elementary form of steam engine. But, instead of being operated by
steam, it was a chemical machine; Smith's trained eyes told him that
the cylinder was really an enormous retort. And he noted with
further perplexity that the prodigious piston-rod not only moved
with terrific speed, but in a strictly back-and-forth motion; its
far end did not revolve.

The agent seemed satisfied with it all. He turned about and
walked--so far as Smith could sense in the usual manner of earth's
humans--back to the dials again. Just then a door opened a short
distance away and another man entered.

Smith would have mistaken him for the employee of some garage. He
was dressed in a suit of greasy blue overalls; and as he advanced
toward the eyes Smith was using, he looked about the room with
practiced glance. He merely nodded to Smith's man, who returned the
nod just as silently; and such was the extreme brevity of it all,
Smith was afterward unable to describe the man.

His agent, thus relieved of his duty temporarily, strolled out
another door, which took him through a narrow corridor and another
door, opening on to some sort of a balcony, or deck. Smith fully