[ 27 2 ] 
the longejl of the two lives, and, in the latter cafe,, 
the value of their joint continuance , ought in reality 
to be fubtradted. I need not fay what prodigious 
errors may often arife from hence, and how unfit 
fuch a method of folution is for practice. The Soci- 
ety in Nicholas-Lane, Lombard-ftreet, for equitable 
a flu ranees on lives and furvivorfhips, have in conftant 
practice fuch queftions as thofe now ftated ; and, had 
they happened to have adopted this method of folu- 
tion, they could not have continued long an advantage 
to the publick. 
Mr. Simpfon, in p. 322. of his Seledt Exercifes, 
fpeaks on this fubje<ft in the following manner. “ I 
“ have been very particular on thefe kinds of pro- 
“ blems; and the more fo, as there has been no 
*< method before published, that I know of, by which 
“ they can be rightly determined. It is true, the 
“ manner of proceeding by firft finding the proba- 
“ bility of furvivorfhip (which method is ufed in my 
former work, and which a celebrated author has 
“ largely infilled on in three fucceffive editions) may 
“ be applied to good advantage when the given ages 
«* are nearly equal ; but then it is certain, that this is 
cc not a genuine way of going to work, and that the 
“ conclulions hence derived are at bed: but near ap- 
“ proximations.” This accurate and excellent mathe- 
matician has here exprefled himfelf much too favour- 
ably, of the method of folution on which I have re- 
marked. In both the cafes I have fpecified, the ages 
are equal ; and yet in. one of them the error is a 
good deal above a third of the true value, and in the 
• other a fifth : And it is obvious, that in cafes where 
three equal lives are taken, the errors will be much 
meater, 
o 
