One is naturally led to suspect that the proportion of male and female children born may depend upon the respective ages of the parents, and that the effect of the proportion of the sexes of the children, following this law, is to render equal the number of the sexes at the average period of marriage. For instance, if the age of the man at the average period of marriage be assumed at thirty years, and that of the woman at twenty-five, it is evident that it will require a greater proportion of male births to make the numbers of the sexes equal at the average period of marriage.

But this reasoning, to have any weight, requires to be supported by a comparison between average periods of marriage in these three places. M. Chabrol, in the "Statistiques de la Ville de Paris," &c., indeed, gives us the average age of the sexes at the period of marriage for a part of France, but I am not aware that any similar calculation is to be found as relating to London or to Naples.

The value of other tables is very much les

* Men in their thirtieth year-women in their twenty-fifth.

sened by their being affected by several causes, so as to prevent us from estimating the agency of any one in particular. At first sight, nothing appears easier than to calculate the average duration of human life, by dividing the amount of population by the number of annual deaths. But to obtain any satisfactory result from such a calculation, it is necessary that the population should be stationary,-neither increasing nor diminishing from internal causes, or by emigration or immigration. For if a population be augmenting from an increased number of births, there will be a larger proportion of the population in the earlier periods of life, which will materially affect the proportion of deaths; the same with respect to a diminution in the number of births. Migrations may affect the mortality either way. Thus, in the metropolis, there is a constant immigration of persons between the ages of twenty and thirty-a cause that would tend to reduce the proportionate mortality.

If the duration of life is estimated by the ages of persons at the period of their death, the same difficulty occurs. Thus, in the county of

Lancaster, population doubled itself within the thirty years preceding 1831. It follows, therefore, that children two to one were born there in the year 1831, as compared with the year 1801; in other words, that such infants then composed a double proportion of the population, in comparison with the class thirty years old, than if the population had been stationary since 1801 ;* a corresponding increase must therefore be expected in the proportion of deaths that take place at an early period of life, without the expectation of life at the period of birth being at all affected by it.

It may be satisfactory to the wedded world to hear, that it is the opinion of those who have turned their attention to the subject,† that the average duration of life is considerably greater to married than to single persons, of both sexes; but though there are statistical tables on this subject in existence, these will not afford us

* Population Return, 1831, preface.

+ Dr. Jasper-De l'Influence du Marriage sur la Durée de la Vie humaine. Annales d'Hygiène publique, 1835. M. Huffeland-L'Art de prolonger la Vie de l'Homme : Paris, 1824. M. Departieux-Essai sur les Probabilités de la Vie humaine, Paris, 1766.

‡ Vide Annales d'Hygiène publique, 1835, No. 28.

the means of ascertaining the proportionate improvement in the duration of life that matrimony occasions, from the circumstance that those who marry are generally in better circumstances than those who remain single.

Many other important facts have not as yet been satisfactorily ascertained by records of a sufficient number of authenticated facts. Such as, for example, the proportion of births that may be expected from marriages contracted between persons in an early period of life as compared with the offspring of marriages contracted between persons more advanced in life. It has been supposed, from a comparison of a limited number of instances, that the difference is very small, but the author is not aware that there is any calculation upon the subject of any value. Indeed very little appears to be satisfactorily ascertained relating to the number of births to be expected from marriages contracted under different circumstances-such as, in a particular condition of society as compared with another-or as regards the comparative prolificness of marriages among different classes of the same community.

From the difficulty therefore of obtaining statistical facts upon which any weight can be safely rested, the author has generally contented himself with adducing one or two of the least objectionable in support of each particular proposition, rather in the way of examples than as proofs. The authority of these might often be strengthened by the addition of a number of tables-individually, perhaps, none of them strictly correct, but if the greater proportion of them united in having one peculiarity, a sufficient number of instances might establish the existence of a rule.

But however satisfactory such a mode of proof might be to the person who himself searches out the cases, these tables would have no manner of authority when brought forward in support of a particular theory. It would have the appearance of packed evidence.

The small number of statistical records adduced may therefore be looked upon rather as forming a primâ facie evidence, than as proofs. And if the opinions herein contained, when tested by the production of a sufficient number