Observations on reversionary payments [electronic resource] : 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, containing a complete set of tables; particularly, Four New Tables, shewing the Probabilities of Life in London, Norwich, and Northampton; and the Values of joint Lives. By Richard Price, D.D. F.R.S.