The assumption explicitly made by General Walker that among the immigrants no influence was yet excited in restriction of population, is also not only gratuitous, but inherently weak; the European peasant who landed (where the great majority have stayed) in the eastern industrial states was thrown suddenly under the influence of the forces just referred to; forces possibly of stronger influence upon him than upon native classes, which are in general economically and socially more stable, On the whole, the better opinion is probably that of a later authority on the vital statistics of the country, Dr John Shaw Billings,i that though the characteristics of modern life doubtless influence the birth-rate somewhat, by raising the average age of marriage, lessening unions, and increasing divorce and prostitution, their great influence is through the transmutation into necessities of the luxuries of simpler times; not automatically, but in the direction of an increased resort to means for the prevention of child-bearing.
The theory of probabilities, which Laplace described as common sense expressed in mathematical language, engaged his attention from its importance in physics and astronomy; and he applied his theory, not only to the ordinary problems of chances, but also to the inquiry into the causes of phenomena, vital statistics and future events.
Conversely, the traces left by a casual set-back, such as famine, war, or an epidemic disease, remain long after it has been succeeded by a period of recuperation, and are to be found in the ageconstitution and the current vital statistics.
But the census returns of 1851 showed a remarkable alteration - a decrease during the previous decade of over 1,500,000 - and since that date, as the following table shows, the continuous decrease in the number of its inhabitants has been the striking feature in the vital statistics of Ireland.
It is true that for practical use in connexion with vital statistics for a given period, the aggregate age-distribution of the countries concerned would be a more accurate basis of comparison, but the wide period covered by the Swedish observations has the advantage of eliminating temporary disturbances of the balance of ages, and may thus be held to compensate for the comparatively narrow geographical extent of the field to which it relates.
