Had God permitted animals to multiply in excess of plants, the entire vegetation would soon have been devoured, and then the animals themselves would of necessity have ceased to exist." "How is it, then," inquired Willis, "with this continual multiplication always going on, the inhabitants of land and sea do not get over-crowded ?" "Why, as regards man, for example, if thirteen or fourteen human beings are born within a given period, death removes ten or eleven others; but though this leaves a regular increase, still the population of the globe always continues about the same." "It may be so, Master Jack, but when I was a little boy at school, I generally came in for a whipping, if I made out two and two to be anything else than four." "And served you right too, Willis; but if the human family did not continually increase, if the number of deaths exceeded continually that of the births, at the end of a few centuries the world would be unpeopled." "Very good; but if, on the other hand, there is a continual increase, how can the population continue the same ?" "Because the increase supposes a normal state; that is to say, the births are only estimated as compared with deaths from disease or old age.

But then there are shipwrecks, inundations, plagues, and war, which sometimes exterminate entire communities at one fell swoop.

Then whole nations die out and give place to the redundant populations of others; phenomena now observed in the cases of the aborigines of Australia and America." "Very true." "No signs of furs yet," cried Fritz, who was every now and then levelling his rifle at the phantoms on shore.
"We need not dread," continued Jack, "ever being hustled or jostled on the earth; life will fail us before space.

There are now eight hundred millions of human beings in existence, and, according to the most moderate computation, room enough for twice that number.

As it is, the most fertile sections of the earth are not the most populous; there are four hundred millions in Asia, sixty millions in Africa, forty in America, two hundred and thirty in Europe, and only seventy millions in the islands and continent of Oceanica!" "To which," remarked Fritz, "you may add the eleven inhabitants of New Switzerland." "Assuming, then, this calculation to be nearly accurate, though authorities vary materially in their computations of the earth's inhabitants, and regarding it in connexion with the average duration of human life, a thousand millions of mortals must perish in thirty-three years; to descend to detail, thirty millions every year, three thousand four hundred every hour, sixty every minute, or ONE EVERY SECOND." "Aye," remarked Willis, "we are here to-day and gone to-morrow." "Suppose, then, that the population of the earth were twice as great, cultivation would be extended, territories that are now lying waste would be teeming with life and covered with fertile fields, but the same beautiful equilibrium would be maintained." "And the inhabitants of the planets," said Fritz, "what are they about ?" "What planets do you mean ?" inquired Willis.
"Well, all in general; the moon, for example, in particular." "The moon," replied Jack, "has, in the first place, no atmosphere.
This we know, because the rays of the stars passing behind her are not, in the slightest degree, refracted; and this proves that neither men, nor animals, nor vegetables of any kind, are to be found in that planet, for they could not exist without air." "That should settle the question," remarked Willis.
"Yes," remarked Fritz; "but some theorists, nevertheless, insist that there may be living creatures in the moon, for all that--of course, differently constituted from the inhabitants of our earth, and susceptible of existing without air.