On Schemes for Providing Annuities for Widows, and for Persons in Old Age; on the Method of Calculating the Values of Assurances on Lives; and on the National Debt. To which are Added, Four Essays on Different Subjects in the Doctrine of Life Annuities and Political Arithmetick. Also, an Appendix and Supplement, Containing Additional Observations, and a Complete Set of Tables ... The Third Edition, Much Enlarged