3. The means of guarding against their extension and effects. 4. The comparative healthiness of different countries and places, climates and seasons. 5. The influence of particular trades and manufactures on the human constitution. 6. They elucidate many important and dubious medical points essential to the perfection of the preventive and curative arts. II. POLITICALLY.--They are a means: 1. Of ascertaining the increment or decrement of the population in every place, and at any period. 2. Of accurately ascertaining the population of the country, and at any period. 3. Of diminishing, if not nearly superseding, the immense expense incurred by a census. 4. Of obviating the difficulties, great expense, and frequent disappointment in proving marriages, births, baptisms, and burials, to which persons who are desirous of establishing legal proof of their identity, descent, consanguinity, &c. are still exposed. 5. The present extensive and beneficial system of assurance on lives, reversionary payments, annuities, and legacy duties on the latter species of testamentary property, is founded on calculations deduced from numerous bills of mortality. 6. The prosperity or decay of commerce, manufactures, or trade of any place, is shown by comparing bills of mortality of different dates. III. MORALLY.--They mark: 1. The prevalence of moral or licentious habits. 2. The diseases of which the inhabitants of a place die; and, consequently, those arising from luxury or intemperance. 3. The effects of the passions on human actions. 4. By knowing where they are most required, the means of correcting such effects may be the more effectually applied. PETERLOO (1819). =Source.=--_Life and Correspondence of Lord Sidmouth_, by Dean Pellew. Vol. III. p. 253. London, 1847. _Letter of Sir Wm. Jolliffe to Thos. G. B. Estcourt._ "9 St. James's Place, April 11th, 1845. "My dear Sir, "Twenty-five years have passed since the collision unfortunately occurred between the population of Manchester and its neighbourhood, and the military stationed in that town, on the 16th of August, 1819.