Note 44 — THE LEVELLING POWER OF RAIN.

Those whose custom it is to regard all theorizing respecting the circumstances revealed by observation as unscientific, may read with profit an extremely speculative passage in Newton’s Principia relating to the probable drying up of the earth in future ages. “As the seas,” he says, “are absolutely necessary to the constitution of our earth, that from them the sun, by its heat, may exhale a sufficient quantity of vapours, which, being gathered together into clouds, may drop down in rain, for watering of the earth, and for the production and nourishment of vegetables; or being condensed with cold on the tops of mountains (as some philosophers with reason judge), may run down in springs and rivers; so for the conservation of the seas and fluids of the planets, comets seem to be required, that, from their exhalations and vapours condensed, the wastes of the planetary fluids spent upon vegetation and putrefaction, and converted into dry earth, may be ultimately supplied and made up; for all vegetables entirely derive their growths from fluids, and afterwards, in great measure, are turned into dry earth by putrefaction; and a sort of slime is always found to settle at the bottom of putrefied fluids; and hence it is that the bulk of the solid earth is continually increased; and the fluids, if they are not supplied from without, must be in a continual decrease, and quite fail at last. I suspect, moreover, that it is chiefly from the comets that spirit comes which is indeed the smallest but the most subtle and useful part of our air, and so much required to sustain the life of all things with us.”