Another small difference betwixt the two hypotheses is, that Monsieur Des Cartes
never thought of making the exterior orb of oily liquids, which the theorist asserts to be absolutely necessary towards the formation of the crust; for if it were not, says he, for the oily liquor which swims upon the surface of the abyss,
the particles of earth which fell through the air had sunk to the bottom, and had never formed the exterior orb of earth. But notwithstanding this, I believe it may be easily made evident (though neither of these systems is true), that the theorist's hypothesis is the worse of the two, which I will prove from his own concessions: for he has already owned that the oily liquor is much lighter than the watery orb. He has mentioned also, that the terrestrial particles when falling from the air, if the orb were only water, would sink to the bottom; and therefore these particles must be heavier than water. From thence
I think it does necessarily follow, that these terrestrial particles must also be heavier than the oily fluid, which is lighter than water, and therefore they will more easily descend through it than they did through water, it being well known that there are several bodies which will suim in water, but sink in oil."[1]
Proceeding on such positions, Keill destroys what has been raised by his adversary, wisely substituting nothing in its stead, except what experiment and demonstration support; the general aim .of the principles he espouses being, that, excepting in so far as we know by experiment the operation of nature, we must take the cosmogony of the earth, either literally as we find it laid down in holy writ, or, admitting our inability to penetrate into its secrets, be content with what is afforded us by experience, demonstration, and rational or certain deduction. Whiston, in his "New Theory of the Earth, from its original to the consummation of all things," maintained, that the Mosaic account of the creation did not give a philosophical account of the formation of the universe, but that it was merely intended, in the most simple and intelligible manner, to give a history of the formation of the globe Ave inhabit; that before being brought into existence as an inhabited world, it had been a comet, which being subject to perpetual reverses from heat to cold, became by the alternate congealing and melting of its surface, covered with a coat of heterogeneous matter or a chaos, within which the solid nucleus formed a great burning globe. This great mass of matter, as the eccentricities of its orbit decreased, became more nearly circular, and the materials ranging themselves according to their gravities, assumed at the period of the "creation n the forms of earth, water, and air. If this theory does not possess any recommendation to our belief superior to that claimed by Burnet, its author had at least the art, to found a greater number of his conclusions on experiments, and to deduce others in a less imaginative manner. Keill treats this adversary with more respect than he affords to the theoretic Burnet, seldom proving his positions "impossible," and generally contenting himself with being sceptical; he allows that the author "has made greater discoveries, and proceeded on more philosophical principles than all the theorists before him have done."
Keill's small work is often referred to as authority by geologists and natural philosophers; it contains many experimental calculations, among which is that estimate of the depth of the sea, on which Breislak in later times founded his celebrated calculation, that there never could have been a sufficient quantity of water in and about our globe to have kept the matter of it at any time in solution. It was considered by many, that Keill had used the venerable doctor Burnet, much his elder in years, a scholar, and a man esteemed for his private virtues, with too much asperity and unbecoming sarcasm. It appears that the
- ↑ Examination 37, 38.
