faintest glimmer of a lamp, the
_Capella_ observed the rules and regulations for preventing collision
at sea. Her port, starboard, and bow lamps were lighted by
electricity, but, in order to guard against possible break-down of
current, oil lamps had also to be trimmed and lighted, ready, should
occasion serve, to take their places.

It was part of Ross's duty to report to the officer of the watch that
these lamps were in order, and also, at regular intervals, that the
navigation lights were burning brightly.

Presently the Sub prepared to take a cross-bearing. He was fairly
certain that the _Capella_ had reached the westernmost limit of her
patrol-ground. From that point she was to proceed due south for 10 sea
miles, and then due east for 20 miles until she fell in with her
"opposite number".

While Barry was thus engaged, Ross noticed a sail about 2 miles distant
on the starboard quarter.

"By Jove!" he muttered as he brought his glass to bear upon the
stranger. "That's a funny rig."

The craft was a "two-sticker". She was square-rigged on the foremast,
carrying fore-topsail and fore-course. No jibs were set; neither, as
far as he could see, was any sail set on the mainmast. The vessel's
sides were painted green with a broad red band.

Even as he kept the craft under observation she starboarded her helm,
shaping a course that would converge upon that of the rearmost of the
two tramps. By so doing she exposed a considerable portion of her
broadside.

Ross gave an exclamation of astonishment. Above the green sides
appeared what was undoubtedly the conning-tower and housed periscope of
a submarine. "Submarine on the starboard quarter, sir!" he reported.

"What!" exclaimed Barry, levelling his telescope. "By Jove, yes! What
luck!"

The unterseeboot had, of course, noticed the _Capella_, and had
mistaken her for a trawler. She realized that she ran a risk in case
the latter might be armed, but, trusting to her disguise, she hoped to
get within torpedo range of the tramp--a vessel of over 3000 tons--sink
her, and make her escape in the confusion that was bound to ensue. On
the other hand, her Kapitan had good reasons for thinking that the
supposed trawler was not one of the armed patrol, since they usually
worked in company. By rigging canvas bulwarks and setting sail upon
dummy masts, he was able to approach with little fear of detection.

"Action!"

Quickly the _Capella's_ crew were at their