I. The object of the first part of this memoir was to determine the normal course of mortality as affected by age alone, without reference to other circumstances.

What we name the law of mortality is not a simple law, but a compendious expression, by which we denote the operation of various laws, physiological, physical, and moral. Of these, the physiological laws are so uniform in their operation that they impress certain characteristic features upon the law of mortality, according to age, which are observed amidst all the diversities which it exhibits under varying circumstances, physical and moral.