A Startling Scientific Prediction.

According to Mr. John Munroe's arliclo in Cassell's Magazine for May, Lord Kelvin startled America by an estimate of tho speedy end of the human race. We are, he calculates, using up our fuel at such a rate that it will all be consumed in five hundred years. That alarm we have heard before. The newer dread is that we are nsiug up our stores of oxygen faster than wo are using our stores of . fuel. In four hundred years' time — at our present rate of use and increase — there will be no more oxygen for us to breathe ! Mr. Munro thus states the great expert's argument : — * When first the earth cooled down from a red-hot state it was surrounded by an atmosphere of bteam, uitrogen, and carbonic acid gas. Evidently it contained little or no free oxygen, »» nono has been found in cavities of tho primitive rocks— for example, grauite. It follows that all, or nearly all, tho free oxygen iv the atmosphere to-day has been produced by vegetation, which, under the action of sunlight, has the power of liberating oxygen from water and carbonic acid. Thus oxygen would pass into the atmosphere, and, in course of time, plants and trees which grow in the soil would continue the preparation of nir for the support of breathing animals. In so doing, the vegetation stored up carbon in the form of wood and foliage, and much of this was preserved as coal, peat, or petroleum oil. ' Now, assuming that there was little or nofree oxygeu at the beginning, the quantity of oxygen in' the atmosphere at any time would be just sufficient to burn up all the living vegetation and its dead remains upon the earth. Even at present this consideration holds good, for, practically speaking, the amount of free oxyg-eu iv cho air is only increased by growing vegetation, and diminished by combustion of vegetable matter. Lord Kelvin reckons our present stock of oxj'gen at over a thousand billion tons, and our stock of fuel therefore at 340 billions of tons, 200,000 tons per present inhabitant : — ' Lord Kelvin, basing bis calculations on the existing rate of increase iv the population aud development of industries requir- i ing fuel, has arrived at the conclusion that J it cannot last for more than 500 years. Thar is not the worst of it. In burning up this fuel the oxygen of the atmosphere will be consumed, and carbonic acid formed, bo that in 400 years, a century before the fuel is dene, tho air will bs unfitted to sustain life. ' The instinctive hopefulness of the average man at once leaps to the conclusion that this swiftly appronching doom can be averted. But how ? — ' With ruin staring us in the eyes, what is to be done ? We must have oxygen to save life, and fuel to save civilisation. Lord Kelvin' lias uttered a timely warning, and our thanks are duo to him ; but can he propose a remedy ? Cultivate enormous quantities of vegetation to increase our store of oxygen. That, he says, is of much more importance than anything we can do to prolong human life on the earth. Let the colonist see to it that he does not extirpate the forest. It will not do to plant only timber trees, for that would diminish the food supply. Fruit trees and forage plants would provide nourishment as well as oxygen.' Otherwise, all animal and human life will become extinct ; and the writer concludes with a dream of an iuanimate world slowly recovering its oxygen, and becoming the home of a race more wise and less wasteful than mankind has proved to bo.