[ 97 ] 
half unity * fubtradied from the quotient, gives 34-^5 
for the expedlatt07i of 20. The expedlation of the 
fame life by Mr. Simpfons Table, formed from the 
bills of mortality of London, is 28.9. 
Thefe obfervations bring me to the principal 
point which I have had all along in view. They 
fuggeft to us an eafy method of finding the number 
of inhabitants in a place from a Table of Obfervations^ 
or the bills of tnortahty for that place, fuppofing the 
yearly births and burials equal. “ Find by the 
“ Table, in the way juft defcribed, the expeilation 
“ of an infant juft born, and this, multiplied by the 
number of yearly births, will be the number of 
‘‘ inhabitants.” At Brefaw, according to Dr. Hal- 
ley’s Table f, though half die under 16, and there- 
fore an infant juft born has an equal chance of living 
only 16 years, yet his expeSlation, found by the rule 
I have given, is near 28 years j and this, multiplied 
by 1238 the number born annually, gives 34,664, 
^ This fubtraaion I’s neceflary, becaufe the divifor ought 
be made as much greater than the number dying annually given 
in the Table, as the expectation^ with ^ unity added, is 
oreater than the, expectation^ on account of the number that will 
die, in the courfe ot the year, out of thofe who are continually 
added, in order to preferve the number of the living the hime. 
In other words : If we conceive the recruit neceffary to fupply 
the wajie of every year to be made always at the end of the 
year, the dividend ought to be the tnedium between the numbers 
living at the beginning and the end of the year ; that is, it ought 
to be taken lejs than the fum of the living in the Table at and 
above the given age, by halp the numoer that die in the year ; the 
effedl of which diminution will be the fame with i\\^ fubU aCtion I 
have dire£fed. 
f Vid. Lowthorp’s Abridgment of the Philoiophical Tranfac- 
tions, vol. III. p. 66g. 
VoL. LIX. O the 
