The rivers had dwindled into rivulets and the seas into vast, shallow marshes.

The heat received from the Sun was only about a twenty-fifth of that which falls on the surface of the Earth, and this was drawn to the cities and collected and preserved under their glass domes by a number of devices which displayed superhuman intelligence.
The dwindling supplies of water were hoarded in vast subterranean reservoirs, and, by means of a perfect system of redistillation, the priceless fluid was used over and over again both for human purposes and for irrigating the land within the cities.

Still the total quantity was steadily diminishing, for it was not only evaporating from the surface, but, as the orb cooled more and more rapidly towards its centre, it descended deeper and deeper below the surface, and could now only be reached by means of marvellously constructed borings and pumping machinery which extended several miles below the surface.
The fast-failing store of heat in the centre of the little world, which had now cooled through more than half its bulk, was utilised for warming the air of the cities, and to drive the machinery which propelled it through the streets and squares.

All work was done by electric energy developed directly from this source, which also actuated the repulsive engines which had prevented the _Astronef_ from descending.
In short, the inhabitants of Ganymede were engaged in a steady, ceaseless struggle to utilise the expiring natural forces of their world to prolong their own lives and the exquisitely refined civilisation to which they had attained to the latest possible date.

They were, indeed, in exactly the same position in which the distant descendants of the human race may one day be expected to find themselves.
Their domestic life, as Zaidie and Redgrave saw it while they were the guests of their host, was the perfection of simplicity and comfort, and their public life was characterised by a quiet but intense intellectuality which, as Zaidie had said, made them feel very much like children who had only just learnt to speak.
As they possessed magnificent telescopes, far surpassing any on Earth, their guests were able to survey, not only the Solar System, but the other systems far beyond its limits as no others of their kind had ever been able to do before.