These data being obtained, it is not difficult to determine the proportion of the annual deaths to the number of the living in each year of age. Then, assuming any number of births, as 1000 or 10,000, it is easy to show how many would die in each year of their age ; and, consequently, how many would survive that year ; which numbers of survivors and of annual deaths, when arranged in the order of the. ages, constitute the desired table of mortality, by which all the most important questions respecting the duration of human life may be easily resolved.
For want of understanding the principles upon which the proper construction of such tables de pends, most of the writers on this subject, many of them men of great merit and industry, have taken much pains to little purpose, and after excessive la- bour, have arrived at false conclusions. Hardly any of them appear to have been aware of the necessity of obtaining the number of the living, as well as of the annual deaths in each interval of age, or that that would greatly enhance the value of Bills of Mor tality, by extending their useful applications.
Dr Price's Essay on the Method of con. structing Tables of Mortality, already twice men tioned in this article, was intended to show bow such tablet might be constructed from registers of the deaths only at all ages ; but the hypotheses he pro ceeded upon can hardly obtain in any real case; and even if they did, his method would only determine the number of the living in the place, at every age; therefore, if it eould be put in practice (which it never can), it would only supersede the necessity of actual enumerations ; and, with the numbers so ob• tained, we should have to proceed as above.
That Essay of Dr Price was an amplification of what Mr Simpson had previously advanced on the subject, with his accustomed accuracy, and contains many just observations on the defects of the tables of mortality that had previously been published ; but so far as it contributed to induce a belief that the determination of the number of the living hi every interval of age, by actual enumeration, was not necessary to the con struction of accurate tables, it must have done harm.
What is here stated will be found demonstrated in the third chapter of Mr Mllae's Tmetite on Anon. ties.
We come now to the