"This is the solar-heat condenser," said Norbert. "You see it in the perfection to which it was lately brought by its inventor, M. Mouchot, Professor of Physics at the Tours Lyceum. It can gather up the solar heat and utilize it in the service of commerce. I believe the inventor hoped that it would, in the first place, tend to facilitate the making of a railway across the Sahara desert. It has already enabled us to bore our well, and, as you shall see when we get to the foot of the mountain, it kindles to a white heat the group of furnaces that fabricate large quantities of glass."

"Do you mean to say," exclaimed Doctor Briet, "that this copper funnel can develop sufficient heat to vitrify sand?"

"You shall judge for yourself," replied Norbert. "But meanwhile let me tell you that in this hot country we receive and absorb, on an average, 38 heat units 1 a minute on a square yard of surface insulation. I have 2000 insulators, and each of them represents ten square yards, which means that I can freely absorb and utilize 760,000 heat units per minute, 45,600,000 heat units per hour, and 456,000,000 heat units in a day of ten hours. Such is the amount of heat placed at our disposal by the sun, and suffered to run to waste by the negligence of man!.

"This is our only heating apparatus. Your cutlets this morning were grilled by the solar heat condenser; the soup and roast meat will be cooked by the same process this evening. The cognac you put in your coffee is distilled by the solar-heat condenser, and in like manner the coffee was refined and infused by the same influence."

"But," said Gertrude, laughingly, "you are obliged always to cook in the day time?"

"Yes, if we are foolish enough to suffer our store of heat to evaporate into space; not so, if we take care to imprison it in a non-conductor, such as a woollen covering, or even a pot full of sand. Virgil does this very cleverly, I assure you!"

"It is marvellous !" cried M. Kersain. "This invention is certainly destined to be of great service in Africa!"

"Much greater than is thought,” replied Norbert. "Remember this is a free and boundless force! ... By the solar action alone it will henceforward be possible to sink artesian wells in the middle of the most arid desert, to get water from any depth, bring it to the surface, and make use of it as we will. . . . Railways can in future traverse the Sahara desert, and the whirr of busy manufactories wake up its silent echoes, while steamers plough the wave without need to trouble about finding fuel. The sun will do it all!... This conic-shaped funnel, once set eastward, the rest will go by itself; and what more easy than to set it so! The lever yonder enables the reflector to be moved backwards and forwards horizontally, while the toothed rack, by setting in motion two cogs, elevates or depresses it vertically.

(Solar-Heat Condenser from 'The Conquest of the Moon' by Andre Laurie)