16， than does AODC in fig.17 with AODC in fig.16.(It is ingeniously argued in Wicksteed's Coordinates of Laws of Distribution， pp.51-2 that rent may be negative.Of course taxes may absorb rent： but land which will not reward the plough will grow trees or rough grass.See above， pp.157-8.)Leroy Beaulieu (R閜artition des Richesses， chap.II) has collected several facts illustrating this tendency of poor lands to rise in value relatively to rich.He quotes the following figures， showing the rental in francs per hectare (2 1/2 acres)of five classes of land in several communes of the D閜artements de l'Eure et de l'Oise in 1829 and 1852 respectively.
Class I.Class II.Class III.Class IV.Class V.
A.D.1829 58 48 34208A.D.1852 80 78 6050 4014.As Roscher says (Political Economy， Sect.CLV)， "In judging Ricardo， it must not be forgotten that it was not his intention to write a text-book on the science of Political Economy， but only to communicate to those versed in it the result of his researches in as brief a manner as possible.Hence he writes so frequently making certain assumptions， and his words are to be extended to other cases only after due consideration， or rather re-written to suit the changed case."15.Carey claims to have proved that "in every quarter of the world cultivation has commenced on the sides of the hills where the soil was poorest， and where the natural advantages of situation were the least.With the growth of wealth and population， men have been seen descending from the high lands bounding the valley on either side， and coming together at its feet." (Principles of Social Science， chap.IV， 4.) He has even argued that whenever a thickly peopled country is laid waste， "whenever population， wealth， and the power of association decline， it is the rich soil.that is abandoned by men who fly again to the poor ones" (Ib.ch.v， 3)； the rich soils being rendered difficult and dangerous by the rapid growth of jungles which harbour wild beasts and banditti， and perhaps by malaria.
The experience of more recent settlers in South Africa and elsewhere does not however generally support his conclusions， which are indeed based largely on facts relating to warm countries.But much of the apparent attractiveness of tropical countries is delusive： they would give a very rich return to hard work： but hard work in them is impossible at present， though some change in this respect may be made by the progress of medical and especially bacteriological science.A cool refreshing breeze is as much a necessary of vigorous life as food itself.Land that offers plenty of food but whose climate destroys energy， is not more productive of the raw material of human wellbeing， than land that supplies less food but has an invigorating climate.
The late Duke of Argyll described the influence of insecurity and poverty in compelling the cultivation of the hills before that of the valleys of the Highlands was feasible， Scotland as it is and was， II， 74-5.
16.In a new country an important form of this assistance is to enable him to Venture on rich land that he would have otherwise shunned， through fear of enemies or of malaria.
17.As Ricardo says (Principles， chap.II) "The compensation given (by the lessee) for the mine or quarry is paid for the value of the coal or stone which can be removed from them， and has no connection with the original or indestructible Powers of the land." But both he and others seem sometimes to lose sight of these distinctions in discussing the law of diminishing return in its application to wines.Especially is this the case in Ricardo's criticism of Adam Smith's theory of rent (Principles， chap.XXIV).
18.Of course the return to capital spent in building increases for the earlier doses.Even where land can be had for almost nothing， it is cheaper to build houses two stories high than one；and hitherto it has been thought cheapest to build factories about four stories high.But a belief is growing up in America， that where land is not very dear factories should be only two stories high， partly in order to avoid the evil effects of vibration， and of the expensive foundations and walls required to prevent it in a high building， that is， it is found that the return of accommodation diminishes perceptibly after the capital and labour required to raise two stories have been spent on the land.
19.See also the writings of Professors Bullock and Landry.
20.In this he will make large use of what is called below the "substitution" of more for less appropriate means.Discussions bearing directly on this paragraph will be found in III， V， 1-3；IV， VII， 8； and XIII， 2： V， III， 3； IV， 1-4； V， 6-8； VIII， 1-5；X， 3； VI， 1， 7； and II， 5.
The tendencies of diminishing utility and of diminishing return have their roots， the one in qualities of human nature， the other in the technical conditions of industry.But the distributions of resources， to which they point， are governed by exactly similar laws.In mathematical phrase， the problems in maxima and minima to which they give rise are expressed by the same general equations； as may be seen by reference to Mathematical Note XIV.
21.The labour-part of the dose is of course current agricultural labour； the capital-part is itself also the product of labour in past times rendered by workers of many kinds and degrees， accompanied by "waiting."
