In consequence of the enormous development of the manufacturing industries, there has been a great increase in the numbers of those engaged in these industries; a large proportion of farm servants has been transformed into wage-earners of the towns. Since men of this latter class commonly marry young, whereas a comparatively small proportion of farm-servants marries, an increase in the marriage-rate has been noticeable during the latter half of the nineteenth century. But since the beginning of the present century a decline in the marriage-rate has become perceptible, and the causes of this decline are more difficult to ascertain. During the nineteenth century the divorce-rate underwent a continuous increase. The divorce-rate is higher in towns than in the country, and higher in thickly populated than in thinly populated countries. _Illegitimate Sexual Relations._--Except as regards the birth of illegitimate children, the only statistical data available regarding illegitimate sexual relations are those which have been obtained by private inquiries. The following are the most important statistics bearing on this question. The annual number of illegitimate births in Europe exceeds 600,000. In most European countries the illegitimate births constitute from 8 to 9 per cent. of the total births, and in every large country in Europe the illegitimate number several millions. From privately collected statistics we learn that in all civilised countries the great majority of unmarried mothers belong to the working classes and to the class of domestic servants; in many countries more than 80 per cent. of unmarried mothers may be thus classified. If from the number of illegitimate children we wish to deduce the probable number of unmarried mothers, we have always to bear in mind the fact that an unmarried mother commonly has one child only, whilst married women have on the average from three to four children. We learn from private statistics that of the fathers of illegitimate children not more than about 45 per cent. belong to the proletariat. The relationship between the number of illegitimate births, on the one hand, and the number of legitimate births and the number of marriages, on the other, is, on one view, the following. The greater the number of marriages, the smaller will be the number of illegitimate births; the greater the average age at marriage, the greater also will be the number of illegitimate births. It is, indeed, extremely probable that a high marriage-rate leads to a low illegitimate birth-rate, and conversely; but we are not justified in regarding such a causal sequence as unquestionable. Variations in the marriage-rate and in the illegitimate birth-rate may be the joint consequences of other common factors. CHAPTER III CHILD MORTALITY