We need not here examine why it is that the human race is less fruitful in great cities than in small towns or in the open country. The fact has long been notorious. We are inclined to attribute it to the same causes which tend to abridge human life in great cities,--to general sickliness and want of tone, produced by close air and sedentary employments. Thus far, and thus far only, we agree with Mr Sadler, that, when population is crowded together in such masses that the general health and energy of the frame are impaired by the condensation, and by the habits attending on the condensation, then the fecundity of the race diminishes. But this is evidently a check of the same class with war, pestilence, and famine. It is a check for the operation of which Mr Malthus has allowed. That any condensation which does not affect the general health will affect fecundity, is not only not proved--it is disproved--by Mr Sadler's own tables. Mr Sadler passes on to Prussia, and sums up his information respecting that country as follows:-- (In the following table numbers appear in the order: Inhabitants on a Square Mile, German. Number of Provinces. Births to 100 Marriages, 1754. Births to 100 Marriages, 1784. Births to 100 Marriages, Busching.) Under 1000 : 2 : 434 : 472 : 503 1000 to 2000 : 4 : 414 : 455 : 454 2000 to 3000 : 6 : 384 : 424 : 426 3000 to 4000 : 2 : 365 : 408 : 394 After the table comes the boast as usual: "Thus is the law of population deduced from the registers of Prussia also: and were the argument to pause here, it is conclusive. The results obtained from the registers of this and the preceding countries, exhibiting, as they do most clearly, the principle of human increase, it is utterly impossible should have been the work of chance; on the contrary, the regularity with which the facts class themselves in conformity with that principle, and the striking analogy which the whole of them bear to each other, demonstrate equally the design of Nature, and the certainty of its accomplishment." We are sorry to disturb Mr Sadler's complacency. But, in our opinion, this table completely disproves his whole principle. If we read the columns perpendicularly, indeed, they seem to be in his favour. But how stands the case if we read horizontally? Does Mr Sadler believe that, during the thirty years which elapsed between 1754 and 1784, the population of Prussia had been diminishing? No fact in history is better ascertained than that, during the long peace which followed the seven years' war, it increased with great rapidity. Indeed, if the fecundity were what Mr Sadler states it to have been, it must have increased with great rapidity. Yet, the ratio of births to marriages is greater in 1784 than in 1754, and that in every province. It is, therefore, perfectly clear that the fecundity does not diminish whenever the density of the population increases. We will try another of Mr Sadler's tables: