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state of London as to healthfulness, number of inhabitants, and its influence on population. The observations I have made may, perhaps, help to shew, how the most is to be made of the lights afforded by the London Bills; and serve as a specimen of the proper method of calculating from them. It is indeed extremely to be wished, that they were less imperfect than they are, and extended
the same, or becoming less, it may increase, the consequence of which will be, that the period of doubling will be shorter than this rule gives it.-According to Dr. Halley's Table, the number of persons between 20 and 42 years of age is a third part of the whole number living at all ages. The prolific part, therefore, of a country may very well be a 4th of the whole number of inhabitants; and supposing four of these, or every other marriage between persons all under 42, to produce one birth every year, the annual number of births will be a 16th part of the whole number of people. And, therefore, supposing the burials to be a 48th part, the annual excess of the births above the burials will be a 24th part, and the period of doubling 17 years.
I must not conclude this note without adding a remark to remove an objection which may occur to some in reading Dr. Heberden's account of Madeira, to which I have referred. In that account 5945 is given as the number of children under seven in the island, at the beginning of the year 1767. The medium of annual births, for eight years, had been 2201; of burials 1293. In six years, therefore, 13,206 must have been born; and if, at the end of six years, no more than 5945 of these were alive, 1210 must have died every year. That is; almost all the burials in the island for six years must have been burials of children under seven years of age. This is plainly incredible; and, therefore, it seems certain, that the number of children under seven years of age must, through some mistake, be given, in that account, 3000 or 4000 too little,
further. More parishes round London might be taken into them: and, by an easy improvement in the parish registers now kept they might be extended through all the parishes and towns in the kingdom. The advantages arising from hence would be very considerable. It would give the precise law according to which human life wastes in its different stages; and thus supply the necessary data for computing accurately the values of all life-annuities and reversions. It would, likewise, shew the different degrees of healthfulness of different situations, mark the progress of population from year to year, keep always in view the number of people in the kingdom, and, in many other respects, furnish instruction of the greatest importance to the state. Mr. De Moivre, at the end of his book on the Doctrine of Chances, has recommended a general regulation of this kind; and observed, particularly, that at least it is to be wished, that an account was taken, at proper intervals, of all the living in the kingdom, with their ages and occupations; which would, in some degree, answer most of the purposes I have mentioned.-But, dear Sir, I am sensible it is high time to finish these remarks. I have been carried in them far beyond the limits I at first intended. I always think with pleasure and gratitude of your friendship. The world owes to you many important discoveries; and your name must live as long as there
is any knowledge of philosophy among mankind. That you may ever enjoy all that can make you most happy, is the sincere wish of,
Your much obliged,
and very humble Servant,
AT Edinburgh, bills of mortality, of the
same kind with those of London, have been kept for many years. I have, since the foregoing letter was written, examined these Bills, and formed a Table of Observations from them, as I found them for a period of 20 years, beginning in 1739, and ending in 1758.-As this is a town of moderate bulk, and seems to have a particular advantage of situation; I expected to find the probabilities of life in it, nearly the same with those at Breslaw, Northampton, and Norwich; but I have been surprized to observe that this is not the case. During the period I have mentioned, only one in 42 of all who died at Edinburgh, reached 80 years of age.-In general; it appears, that the probabilities of life in this town are much the same, through all the stages of life, with those in London, the chief difference being, that after 30, they are rather lower at Edinburgh.-It is not difficult to account for this. It affords. I think, a striking proof of the pernicious effects arising from uncleanliness, and crowding together on one spot too many inhabitants. At Edinburgh, Mr. Maitland says, "the build
ings, elsewhere called houses, are denomi"nated lands, and the apartments, in other places named stories, here called houses, are so many freeholds inhabited by different families; whereby the houses are so excessively crowded with people, that the inhabitants of this city may be justly pre"sumed to be more numerous than those of some towns of triple its dimensions." See Maitland's History of Edinburgh, p. 140.
In the year 1748, the whole number of apartments or families in the city and liberties of Edinburgh, was 9064. This Mr. Maitland mentions as the result of particular examination, and undoubtedly right. ib. p. 217, 218. In 1743, an accurate account was taken, by the desire of this writer, of the number of families and inhabitants in the parish of St. Cuthbert. Ib. p. 171. The number of families was 2370, and of inhabitants at all ages, 9731. The proportion, therefore, of inhabitants to families, was 4 to 1; and, supposing this the true proportion for the whole town, the number of inhabitants was 4, multiplied by 9064, or 37,162. The yearly medium of deaths in the town and liberties for eight years, from 1741 to 1748, was 1783, 16. p. 220 and 222. And, consequently, one in 20 died annually.
Mr. Maitland, though possessed of the data from which these conclusions necessarily followed, has made the number of inhabitants 59,120, in consequence of a disposition to