Another investigation into the mortality experience of life assurance companies by the Institute of Actuaries will, in all probability, take place at no very distant period; and I think it is extremely desirable that this subject should previously be ventilated in the pages of the Journal. A very elementary acquaintance of that branch of the doctrine of probabilities which treats of the law of “Errors of Observation” will suffice to enable anyone to follow my reasoning in the following pages, and to form his own opinion as to whether the conclusions which I have arrived at are right or wrong.