a black curtain of clouds
swept across the sky, and in an incredibly short time the lightning
flickered for a few minutes through the trees, and then came in blinding
flashes, accompanied more than followed by peal upon peal of thunder
which seemed to shake the island to its foundation.

Worse still was to follow. Just as the lightning was flashing and
quivering among the trees, and the thunder was at its loudest, the rain
came down. It had approached from the sea with, a dull hissing sound
which grew louder and louder, till with startling force the wind which
bore it on its wings flung it as it were with a tremendous force upon
the mountain slope, whipping the boughs and tearing the leaves from the
twigs, pouring away with terrific violence, and rushing downward into
the gully, which soon became filled with a roaring torrent which swept
all before it.

This was the first example the doctor had encountered of the power of a
tropical storm, and he was glad to shelter himself and his four
companions beneath an overhanging ledge of lava rock--a poor protection,
but such as it was it saved them from much of the force of the storm.

The downpour ceased as suddenly as it had commenced, the tempest
sweeping over the island to pass on to the ocean and be dissipated
there, so that in little more than an hour the sun was shining down
through the trees again, where the drenched earth was spangled as it
were with jewels.

But the task of continuing the search was now made excessively
difficult. The ground was slippery in the extreme, save where the lava
had been washed bare, and at almost every step the water-laden boughs
poured down a fresh shower upon them. The labour was terrible, for now
it was as if they were forcing their way through a bath of hot vapour
which was enervating in the extreme.

But they struggled on hour after hour, vainly seeking for some trace of
the missing ones--a task which would have baffled the keenest-eyed Red
Indian, for the rain had swept away every footprint, and when at rare
intervals a broken branch or torn-off leaf-covered twig was found, it
was as likely to have been the work of the storm as of any one passing
through.

Faint with an exhaustion he would not own to, the doctor was still
urging or cheering his men on, when the dull concussion of a gun and the
following echoes announced that those on the yacht were impatient for
their return.

"Signal to come back, sir," said Lenny desp