Presently he looked at his watch.

“Almost eleven,” he said, “we must have passed the light by this time.”

“I don’t know,” said Peggy helplessly; “if only the chart marked that bell buoy—­but it doesn’t.”

She again scrutinized the chart pinned before her on the sloping slab designed for such purposes.  But no bell buoy was marked on it as being located anywhere near where they estimated they must be drifting.  Drifting, however, is not quite the correct word.  An aeroplane cannot drift.  Its life depends upon its motion.  The instant it stops or decreases speed beyond a certain point, in that same instant it must fall to the earth.

This fact is what made the position of the young sky cruisers particularly dangerous.  Although the gauge showed that they had plenty of gasoline, the supply—­even with the use of the auxiliary tanks—­would not hold out indefinitely.  If the fog did not lift, or they did not land, sooner or later they must face disaster.  Worse still, they were—­or believed they were, navigating above the sea.

Had the Golden Butterfly been fitted with pontoons like some of the Glen Curtiss machines, this would not have been so alarming.  But a descent into the ocean would inevitably mean a speedy death by drowning.

Suddenly voices struck through the smother all about them.  They seemed to come from below.

“It’s thick as pea soup, captain!”

“Aye, aye; I’ll be glad when we’re out of it I kin tell yer.  This bay’s a bad place ter be in er fog.”

“A ship,” cried Jimsy.  “Quick, Peggy,” he almost yelled the next instant.  “Set your rising levers.”

The girl swiftly manipulated the machinery that sent the Golden Butterfly on an upward course.

But it was only just in time that this maneuver was carried out.  All of them had a glimpse for an instant of the gilded ball on the main-mast head of the vessel beneath them.  For an instant Peggy’s watchful eye had been deflected from the height gauge, and she had allowed the Golden Butterfly to drop almost on the top of some coasting vessel’s mast.

The danger over, they could not help laughing at the whimsical adventure.

“Just to think how utterly unconscious those fellows were of the fact that three human beings were hovering right above them and listening to every word of their conversation,” chuckled Jimsy; “isn’t it queer?”

A little while later a steamer’s whistle boomed through the fog beneath them, but as the altitude register showed five hundred feet, they did not bother about it.

“At all events we know we’re still above the water and not in danger of colliding with any church steeples,” said Jess, and she found consolation in the thought.

“Have you any idea at all as to the direction of the light, Peggy?” inquired Jimsy at length.

“I—­I really don’t know,” confessed Peggy, with a gulp; “everything’s mixed up.  It’s so thick I can’t tell anything and I’m deathly afraid of running into the lighthouse by mistake.”