14.In the first edition of his essay， 1798， Malthus gave his argument without any detailed statement of facts， though from the first he regarded it as needing to be treated in direct connection with a study of facts； as is shown by his having told Pryme (who afterwards became the first Professor of Political Economy at Cambridge) "that his theory was first suggested to his mind in an argumentative conversation which he had with his father on the state of some other countries" (Pryme's Recollections， p.66).American experience showed that population if unchecked would double at least once in twenty-five years.He argued that a doubled population might， even in a country as thickly peopled as England was with its seven million inhabitants， conceivably though not probably double the subsistence raised from the English soil： but that labour doubled again would not suffice to double the produce again."Let us then take this for our rule， though certainly far beyond the truth；and allow that the whole produce of the island might be increased every twenty five years [that is with every doubling of the population] by a quantity of subsistence equal to that which it at present produces"； or in other words， in an arithmetical progression.His desire to make himself clearly understood made him， as Wagner says in his excellent introduction to the study of Population (Grundlegung， Ed.3， p.453)， "put too sharp a point on his doctrine， and formulate it too absolutely." Thus he got into the habit of speaking of production as capable of increasing in an arithmetical ratio： and many writers think that he attached importance to the phrase itself： whereas it was really only a short way of stating the utmost that he thought any reasonable person could ask him to concede.What he meant， stated in modern language， was that the tendency to diminishing return， which is assumed throughout his argument， would begin to operate sharply after the produce of the island had been doubled.Doubled labour might give doubled produce： but quadrupled labour would hardly treble it： octupled labour would not quadruple it.
In the second edition， 1803， he based himself on so wide and careful a statement of facts as to claim a place among the founders of historical economics； he softened and explained away many of the "sharp points" of his old doctrine， though he did not abandon (as was implied in the earlier editions of this work) the use of the phrase "arithmetical ratio." In particular he took a less despondent view of the future of the human race； and dwelt on the hope that moral restraint might hold population in check， and that "vice and misery，" the old check， might thus be kept in abeyance.Francis Place， who was not blind to his many faults， wrote in 1822 an apology for him， excellent in tone and judgment.
Good accounts of his work are given in Bonar's Malthus and his Work， Cannan's Production and Distribution， 1776-1848， and Nicholson's Political Economy， Bk.1， ch.XII.
15.Taking the present population of the world at one and a half thousand millions； and assuming that its present rate of increase (about 8 per 1000 annually， see Ravenstein's paper before the British Association in 1890) will continue， we find that in less than two hundred years it will amount to six thousand millions；or at the rate of about 200 to the square mile of fairly fertile land (Ravenstein reckons 28 million square miles of fairly fertile land， and 14 millions of poor grass lands.The first estimate is thought by many to be too high： but， allowing for this， if the less fertile land be reckoned in for what it is worth， the result will be about thirty million square miles as assumed above).Meanwhile there will probably be great improvements in the arts of agriculture； and， if so， the pressure of population on the means of subsistence may be held in check for about two hundred years， but not longer.
16.Of course the length of a generation has itself some influence on the growth of population.If it is 25 years in one place and 20 in another； and if in each place population doubles once in two generations during a thousand years， the increase will be a million-fold in the first place， but thirty million-fold in the second.
17.Dr Ogle (Statistical Journal， Vol.53) calculates that if the average age of marriage of women in England were postponed five years， the number of children to a marriage， which is now 4.2would fall to 3.1.Kor鰏i， basing himself on the facts of the relatively warm climate of Buda Pest， finds 18-20 the most prolific age for women， 24-26 that for men.But he concludes that a slight postponement of weddings beyond these ages is advisable mainly on the ground that the vitality of the children of women under 20 is generally small.See Proceedings of Congress of Hygiene and Demography， London 1892， and Statistical Journal， Vol 57.
