They had reached a turn in the valley, where once more a grand view of the mountain chain spread before them, far as eye could reach, purple mountains, and beyond them mountains that seemed to be of silver, where the snow-capped their summits.

But among them were several whose regular form took the professor’s attention directly, and he pointed them out.

“Old volcanoes,” he said quietly.

“Where?” cried Lawrence. “I want above all things to see a burning mountain.”

“You can see mountains that once burned,” said the professor; “but there are none here burning now.”

“How disappointing!” cried Lawrence. “I should like to see one burn.”

“Then we must go and see Vesuvius,” cried Mr Burne decisively. “He shall not be disappointed.”

“I think the young effendi may perhaps see one burning a little here,” said Yussuf quietly. “There are times when a curious light is seen floating up high among the mountains. The peasants call it a spirit light, but it must be the sulphurous glare rising from one of the old cones, above some of which I have seen smoke hanging at times.”

“Why, Yussuf, you are quite a professor yourself, with your cones, and sulphurous, and arguments,” cried Mr Burne.

“A man cannot be wandering all his life among nature’s wonders, effendi, and showing English, and French, and German men of wisdom the way, without learning something. But I will watch each night and see if I can make out the light over the mountains.”