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 despondently. "Yes, but we can't go back without finding them first," said the doctor angrily. "Who is to face Sir John Meadows and tell him we have failed in our duty of protecting his son?" No one answered, and the silence was broken by the dull thud of another gun. "It is of no use, I can't return while it is light, but the summons must be answered. Here, Lenny, go back and tell Sir John what has happened, and that we are searching in every direction." "Me, sir?" cried the man with a look of horror; "I couldn't do it, sir." "You must. You have been out all day, and must be done up." "Me, sir! My mate's ever so much worse nor me. Send him." "G'orn with you," cried the other sailor who had been with them since the first start; "why I arn't half so done as he is, sir."