it--"

"I didn't know that," observed Mary's father slowly. "Do you suppose
it's a test of another gas helmet that Tom has asked us out to see
to-night?"

"I hardly think so," said Ned. "He wouldn't wait until after dark for
that. This is something big, and Tom must intend to have it out in the
open. He probably waited until after sunset so the neighbors wouldn't
come out in flocks. There's been a lot of talk about what is going on
in Shop Thirteen, especially since the arrest of the German spies, and
the least hint that a test is under way would bring out a big crowd."

"I suppose so," agreed Mr. Nestor. "Well, I'm glad to know that Tom is
doing something for Uncle Sam, even if it's only helping with gas
helmets. Those Germans are barbarians, if ever there were any, and
we've got to fight them the same way they fight us! That's the only way
to end the war! Now if I had my way, I'd take every German I could lay
my hands on--"

"Father, pretzels!" exclaimed Mary.

"Eh? What's that, my dear?"

"I said pretzels!"

"Oh!" and Mr. Nestor's voice lost its sharpness.

"That's my way of quieting father down when he gets too strenuous in
his talk about the war," explained Mary. "We agreed that whenever he
got excited I was to say 'pretzels' to him, and that would make him
remember. We made up our little scheme after he got into an argument
with a man on the train and was carried past his station."

"That's right," admitted Mr. Nestor, with a laugh. "But that fellow was
the most obstinate, pig-headed Dutchman that ever tackled a plate of
pig's knuckles and sauerkraut, and if he had the least grain of common
sense he'd--"

"Pretzels!" cried Mary.

"Eh? Oh, yes, my dear. I was forgetting again."

There was a moment of merriment, and then, after the talk had run for a
while in other and safer channels, Mr. Damon made the announcement:

"I think we're about there. We'll be at Tom's place when we make the
turn and--"

He was interrupted by a low, heavy rumbling.

"What's that?" asked Mr. Nestor.

"It's getting louder--the noise," remarked Mary. "It sounds as if some
big body were approaching down the road--the tramp of many feet. Can it
be that troops are marching away?"

"Bless my spark plug!" suddenly cried Mr. Damon. "Look!"

They gazed ahead, and there, seen in the glare of the automobile
headlights, was an immense, dark body approaching them from across a
level field. The rumble and roar became more prono