As the Table shows, Ceres is so small that the Earth exceeds it in volume 5000 times; even the Moon is 90 times as large. The mass of Ceres is not known; being so small, its density is probably less than that of the Moon, so that the Earth may easily outweigh it 10,000 times. The unfavourable conditions resulting from smallness of size that the Moon presents are therefore exaggerated exceedingly in the case of Ceres; its atmosphere must approach in tenuity what we should regard as a vacuum in a terrestrial laboratory, and water as a liquid be entirely unknown. Its distance from the Sun is another hostile factor; for in consequence it receives per unit of surface only 13 per cent of the light and heat that falls on the Earth; its maximum temperature under a zenith Sun will fall far below freezing-point, the minimum on the dark side will approach the absolute zero. With Ceres the whole of the asteroidal family can be dismissed as possible abodes of life. No astronomer can regard them as such. Yet they have their lesson to teach. Life can exist on the Earth only on the upper face of its crust, and in a very thin film of air and water; but the enormous solid bulk within, inert though it be, that supports the stage on which the great drama of life is played, is as really essential as air and water themselves. If that bulk were much smaller and less massive life could find no place upon its surface. CHAPTER X THE MAJOR PLANETS It is a striking change to pass from Ceres, the giant of the minor planets, to Jupiter, the giant of the major planets. Instead of a world that the Earth exceeds in volume 5000 times, we are confronted by one that exceeds the Earth 1400 times. Ceres, when viewed through a large telescope, is just able to present a perceptible disc; Jupiter offers the largest shown by any heavenly body after the Sun and Moon. And that disc is one that never fails to charm the attentive student, for it abounds in colour, movement and change. The late Prof. James Keeler, an observer of the first rank, having the advantage of observing the planet from the summit of Mt. Hamilton and with the great 36-inch telescope of the Lick Observatory, thus describes the aspect of the planet in 1889.