Page:Popular Science Monthly Volume 5.djvu/510

494 person consumes two pounds a day of this gas, or over seven hundred pounds a year, or some twenty-five tons in the allotted period of seventy years; and the thousand million human beings upon the earth are all busy, day and night, from birth to death, in altering the constitution of the air at the same rapid rate. And what man is doing, all the multitudinous tribes of inferior life, in the sea, on the land, and in the air, are doing also. Besides this, the great operations of combustion, fermentation, and decay, upon the globe, are carried on by the insatiable affinities of the same ubiquitous agent. It has been calculated that the oxygen required daily to maintain the course of terrestrial transformations is no less than eight thousand million pounds, or seven millions one hundred forty-two thousand eight hundred and forty-seven tons. And, though this is probably an extreme under-estimate, we have seen that the stock of free oxygen in the air is so vast that it would require millions of years for this rate of consumption to make a sensible impression upon it, even if the counter-changes of the vegetable kingdom, by which the balance is constantly restored, should altogether cease.

Such is the grandeur of the part played by this wonderful element of Nature which has now been known exactly a hundred years. In his beautiful lecture which forms the opening article of our present number, Dr. Draper has vividly portrayed the office of oxygen in relation to the scheme of terrestrial life, and to this nothing needs to be added. But it is fit, on the present occasion, to give emphasis to the fact that, up to the time of Priestley, mankind were as absolutely ignorant of these things as if they had been destitute of all capacity to understand them. The human race had indeed run a vast career of intellectual activity, and had exploited numberless fields of thought with great results. Forms of religion and systems of philosophy had grown and decayed; numerous arts were perfected and forgotten; literatures were cultivated, exhausted, and passed by; empires and civilizations had flourished and faded, and for many thousands of years the world's greatest minds had been speculating, questioning, and inventing, before the man appeared who first explained the constitution of the air, and who first gave a rational answer to the question, "What is the breath of life?" At a superficial glance we should infer that there had been an enormous waste of precious intellectual force in all those historic ages over futile and worthless subjects, and that, while investigating with infinite assiduity every thing that was remote and impossible, the vital and immediate matters of daily and intimate concern had been systematically shunned as objects of study. But the intellectual evolution of man has conformed to a method, and Nature seems to have been no more economical of her mental than of her material resources. There is a prodigality in her ways which a narrow philosophy cannot comprehend. Of her profusion of flowers, but few issue in fruit; of her myriads of eggs, but few are hatched; of her numerous tribes of life appearing in the remote past, multitudes are extinct; and, of the achievements of her intellect, the great mass is lost in oblivion. But, through all her seeming waste, Nature has, nevertheless, a grand economy. She gives the widest chances, under a system which favors the best; the failures are rejected and the fittest survive. Through apparently boundless waste, with infinite deliberation, she works onward and upward to a better state of things, and in the mental world no less than in the physical, through interminable defeats and failures, and a prodigious amount of empty and fruitless effort, solid and