[ 335 ] 
and {hall therefore forbear to exemplify on a fubjedt, 
with which you are fo well acquainted. 
The advantages attending the determination of 
thofe things, by calculation, rather than by cuftom, 
being therefore confidered as evident, it may feem 
ftrange, that, notwithstanding many of thefe tenures 
have lubfifled from the very origin of private pro- 
perty in thefe kingdoms, yet we do not meet with fo 
much as an attempt towards computing their values, 
till that of the late juffly celebrated Dr. Halley, by 
the affiftance of the bills of mortality of Breflaw in 
Silefia, which was foon followed by Mr. De Moivre’s 
truly admirable hypothecs, that the decrements of 
life may be efteemed nearly equal, after a certain 
age. 
It has been the opinion of fome authors, that, 
fince his hypothecs was originally derived from the 
Breflaw obfervations, it cannot be near fo well ad- 
apted to the inhabitants of thefe kingdoms, as what 
has been derived from the bills of mortality of Lon- 
don. But this argument doth not, as I conceive,, 
appear to be conclufive ; firft, 
Becaufe thofe bills, as hitherto kept, are not well 
adapted to anfwer this purpofe. 
Secondly, Becaufe the manner, in which the in- 
habitants of London, and thofe of moft of the coun- 
try towns and villages, live, their occupations, diet* 
and diverfions, nay the very air they breathe, are as 
different, as thofe of London, and Breflaw, can pof- 
fibly be ; and, confequently, fo muff the times of 
their diiTolution. All which has been, with a great 
deal of clearnefs, evinced by the gentleman above 
quoted. 
Thirdly, 
