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.