A good deal of misconception prevails, on the part of many interested in the science of life contingencies, in regard to the expressions usually assigned as the measures of the probabilities of the different orders of survivorship among two or more lives. It seems to be supposed that these expressions are little better than rude approximations, adopted from convenience or necessity, depending on no definite principles, and consequently giving results but little entitled to confidence. It appears to me that these notions are attributable, in no small degree, to the manner in which the expressions in question have been spoken of by the writers, Messrs. Morgan and Baily, by whom they were first deduced.