heavily laden trucks were passing into steamship
piers, and guards and watchmen at every entrance were closely
scrutinizing all who approached.

The four observers walked slowly along, studying every foot of the way.
High fences had been built here and there to hide what was going on
behind them. Covered ways led from railway terminals to pier sheds so
that none could see what had come by train. Even the gangways to the
ships were screened. Every precaution had been taken to baffle curious
eyes.

"They've done their best," commented Captain Hardy, "but they can't
screen a ship on the river, and the Germans know when our transports
sail, even if they don't know what's in them. Any one with a good
glass can look out from any house along the river front and see clearly
every move made by a steamer. Let's take a stroll among these houses."

They left the bustling water-front and passed to the higher ground
where stood the city proper. It was like most other American
municipalities--dirty, dingy, and unattractive, a hotchpotch of
buildings with no architectural unity. But it had one feature
possessed by few cities--an outlook on a great and busy harbor.

As the boys stood looking at the rolling Hudson below them, watching
the ferry-boats come and go, like huge shuttles in a giant loom,
following the movements of steamers, and tugs and tow-boats, and
tracing the circling flight of the gulls, they forgot entirely the
errand that had brought them. Presently their leader broke the silence.

"We shall have to get to work," he said.

Starting at one end of the street, they walked slowly along its entire
length, studying every house that fronted on the river. They saw at
once that their task was hopeless. Square after square the houses
stretched in unbroken blocks. A hundred spies might be living in those
houses and no one be the wiser. A hundred wireless outfits might be
flashing messages among the clothes-lines on the roofs and only a roof
to roof survey would reveal the fact. But it was not necessary to run
even so slender a risk of discovery. As the wireless patrol knew only
too well, an aerial would work with great efficiency even though it
were strung in a chimney or erected entirely within doors. Yet the
little party continued its investigation until dusk, scanning every
window whence a glass might be directed toward the river, and threading
alleys and scrutinizing the wires of roofs and yards. But nowh