“How hot it is here!” said Leo, gasping for breath.

“Yes, my dear fellow, there’s no doubt of that; the heat is tremendous.  Now some of your thermometers go no higher than one hundred and thirty, while ours can ascend to three and four hundred; that is, for the common air of our dwellings.  Of course the heat demanded by many of our experiments is practically incalculable; for instance—­”

“Oh, get me out of this!” entreated Leo.

“Here, step into this niche, put your mouth to this opening”—­and Knops pointed to one of many silver tubes which projected near them—­“now breathe.  Is not that refreshing?”

“Yes,” said Leo, reviving, as he took a long draught of fresh cool air.  “How do your people endure such heat?”

“They are used to it; besides, they can come to these little tubes, as you have done, whenever they please.”

“Where does this air come from?”

“It is pure oxygen; we manufacture it, and here is a lump of pure carbon which we also manufacture,” and he laid in Leo’s hand what looked like a drop of dew.  It was a diamond of exquisite lustre.

As Leo looked with surprise and admiration at it, an elf came staggering up to the niche.  After breathing the oxygen he turned to Knops with a heart-rending cry.

“I have lost it—­lost it, Master Knops.”

“Lost what, Paz?”

“The finest stone I ever made, and I have been years at it.”

“How did that happen?”

“Burned it too long—­look!” and he produced in his spidery hand a small mass of charcoal.

“Never mind, Paz; better luck next time,” said Knops, kindly.

“No, I am no longer fit for the profession; such a mistake is inexcusable.  I cannot hold up my head among the others.  I meant that diamond for our King’s tiara or the Queen’s necklace—­bah!  Please, Master Professor, put me among the miners, or take me for your valet.  I care not what I do.”

“You are depressed just now; wait awhile.”

“No, I must go.  I have broken my crucible and put out my furnace.  I will not stay to be scorned.”

“Come with me, then, and I will see what I can do for you.”

“He may be useful to us,” said Knops to Leo, adding, “we never allow these diamonds to be put in the quartz beds; they are all reserved for our own particular uses.  It takes so long a time to make them that only elves of great patience and a certain quiet habit of mind are trained to the task.  Look!”

He pointed towards what appeared to be a glittering cobweb hanging from a projection on the wall.  It was composed of silver wires, on which were strung numbers of small but most exquisite gems, each of which sparkled and flashed with its imprisoned light.

“In the same way,” he resumed, “all the pearls we use are of our own cultivation, if I may use the term.  We secure the oysters and insert small objects within the shells, generally a seed-pearl of insignificant size, leaving it to be worked upon by the living fish; when enough time for the incrustation has elapsed we find our pearls grown to a remarkable size, of rarest beauty and value.  These processes are not unknown to man, but men are so clumsy that they seldom succeed in perfecting them.”