One element underlying the whole theory of Life Contingencies is that of a Series. Thus in the Life Table we have a collection of the more usual and elementary functions, every column forming a series, and it will at once suggest itself that as soon as the actual calculation of any problem is faced, we must sooner or later arrive at a Series, and the solution of the problem will finally depend on our ability to deal with this Series. The same is obviously true of other branches of our Science, such as those derived from statistics of Sickness, of Marriage and of Issue, and, of course, in the purely algebraical theory of Compound Interest.