ON LIFE CONTINGENCIES. l65 



cient to give the mean duration of life with considerable 

 approach to exactness. This is confirmed by the 

 results of various tables, from which it appears that 

 when the individuals composing an observation are of 

 the same country, and under the same general circum- 

 stances, the results of such tables come very near to each 

 other. 



The reader who desires to know the history of tables 

 of mortality should consult the articles MORTALITY and 

 ANNUITIES in the new edition of the Encyclopaedia 

 Britannica, both from the accurate pen of Mr. Milne, the 

 author of the Carlisle tables. I cannot, in this work, 

 pretend to give more than a slight summary of results 

 connected with life contingencies, such as may guide the 

 reader who understands the main points of the theory 

 of probabilities to safe conclusions. 



From some tables made from observations at Breslau, 

 De Moivre concluded that the following hypothesis, 

 namely, that of 86 persons born one dies every year 

 till all are extinct, would very nearly represent the 

 mortality of the greater part of life, and that its errors 

 would nearly compensate one another in the calculation 

 of annuities. The Northampton tables of Dr. Price, 

 which have been used by most of the insurance offices, 

 very nearly represent this hypothesis at all the middle 

 ages. But both give much too large a mortality for 

 the circumstances of the last half century, as is proved 

 by all the tables which have been lately constructed. 

 The greater part of the difference, I have no doubt, is 

 due to the real improvement of life which has taken 

 place, from the introduction of vaccination, more tem- 

 perate habits of life *, better medical assistance, and 

 greater cleanliness in towns. We may now state, as a 

 much nearer approximation to the mortality of the 



* I must be understood, here, as speaking particularly of the middle 

 classes, in English towns and cities. Most of the tables have a majority of 

 this class, and there is not any very precise information on the mortality 

 of the labouring classes, or in the inhabitants of the country as distin- 

 guished from those in towns. With regard to the point on which this 

 note is written, all old persons remember the time when what we should 

 now call hard drinking was almost universal. 

 M 3 



