The modern phase of this movement, soon after which our precise knowledge begins, may be said to date from the industrial expansion, due to the introduction of machinery, which Professor Marshall places in England about the year 1760. That represents the beginning of an era in which all civilised and semi-civilised countries are still living. For the earlier centuries we lack precise data, but we are able to form certain probable conclusions. The population of a country in those ages seems to have grown very slowly and sometimes even to have retrograded. At the end of the sixteenth century the population of England and Wales is estimated at five millions and at the end of the seventeenth at six millions--only 20 per cent. increase during the century--although during the nineteenth century the population nearly quadrupled. This very gradual increase of the population seems to have been by no means due to a very low birth-rate, but to a very high death-rate. Throughout the Middle Ages a succession of virulent plagues and pestilences devastated Europe. Small-pox, which may be considered the latest of these, used to sweep off large masses of the youthful population in the eighteenth century. The result was a certain stability and a certain well-being in the population as a whole, these conditions being, however, maintained in a manner that was terribly wasteful and distressing. The industrial revolution introduced a new era which began to show its features clearly in the early nineteenth century. On the one hand, a new motive had arisen to favour a more rapid increase of population. Small children could tend machinery and thereby earn wages to increase the family takings. This led to an immediate result in increased population and increased prosperity. But, on the other hand, the rapid increase of population always tended to outrun the rapid increase of prosperity, and the more so since the rise of sanitary science began to drive back the invasions of the grosser and more destructive infectious diseases which had hitherto kept the population down. The result was that new forms of disease, distress, and destitution arose; the old stability was lost, and the new prosperity produced unrest in place of well-being. The social consciousness was still too immature to deal collectively with the difficulties and frictions which the industrial era introduced, and the individualism which under former conditions had operated wholesomely now acted perniciously to crush the souls and bodies of the workers, whether men, women, or children.