hundreds of planetoids have now been discovered between the orbits of Mars and Jupiter, and probably many hundreds more remain to be discovered; but of one thing we are certain, that none of the planetoids yet to be discovered will be of the same rank as either of those two guardians, Mars and Jupiter, who revolve on the confines of the planetoidal zone. Indeed, Ceres, the planetoid first discovered, has a greater mass than the aggregate of all discovered since, and probably of all that exist in the zone.

Water is essential for life here, but the quality in water which restricts the range of terrestrial life is that it freezes at 0° Centigrade, and boils at 100° Centigrade; it is only in the liquid state during the intermediate range of 100 degrees. In order to extend the range for living organisms, we should have, therefore, to discover a new vehicle, that, possessing all the other qualities of water, is not restricted to the liquid state within the same limits. But we are at once met with the difficulty that the first essential for the vehicle is that it should be abundant, and there are no other elements more abundant than hydrogen and oxygen. This new vehicle must, like water, be both neutral and stable, or it would itself interfere with the highly unstable compounds that are a necessity for metabolism. And, if we could find this new vehicle, liquid at temperatures outside the 0° to 100° Centigrade, have we any reason to suppose that protoplasm itself would be able to endure these outlying temperatures? Looking through the range of substances available, we can only say that none other presents itself as approaching water in suitability for its essential office. If we, ourselves, were able to create a vehicle, could we imagine one more perfectly suited?