to Age, and the "English Life Table" 27 



years is shown to differ very little from that of the general po- 

 pulation at the same interval of age. If the fact is in accord- 

 ance with the observation, the result may be ascribed to the free 

 interchange of town and country population at this interval of 

 age. There commonly occurs at this interval of age a great in- 

 flux of population into the large towns from the surrounding- 

 country. A portion of these immigrants become a part of the 

 permanent population of these large towns ; another portion re- 

 turns and again form part of the country population. The 

 greater the competition and the greater the freedom of in- 

 terchange of the country with the town population, the more 

 will the mortality of the two classes of population, between the 

 ages of 10 and 30 years, approach to equality. 



The English Life Table for males, which, was published in 

 1864, coincides nearly at all ages with my theoretical Table of 

 "Mean Mortality/' published in 1832, and with the Table de- 

 duced from my formula of 1866. This will be seen on inspec- 

 tion of Table II. hereunto annexed, in which is exhibited for 

 quinquennial intervals of age, according to the three Tables, the 

 numbers surviving and the numbers dying relative to 1000 sur- 

 vivors at the age 12 years. The differences between the English 

 Life Table and the two theoretical Tables are small; and these 

 differences are of no importance, because they are equalled, if not 

 exceeded, by the errors of observation and errors of calculation 

 involved in the English Life Table. 



In Table IV. (hereunto annexed) a comparison is made for 

 decennial intervals of age, from the age 15 to the age 95 years, 

 of the observed rates of mortality of the total male population 

 of England for the seventeen years 1838-1854, with the corre- 

 sponding rates exhibited by the English Life Table. In three 

 out of the eight decennial intervals of age compared, there is a 

 considerable discrepancy between the rates observed and the 

 rates exhibited by the English Life Table. The three errors of 

 calculation are all in the same direction, and are in diminution 

 of the rates of mortality observed. The error at the decennial 

 interval of age 15 to 25 is 8*5 per cent., at the interval from 

 75 to 85 it is 7*4 per cent., and at the interval from 85 to 95 

 years it is 13*1 per cent. 



In Table V. (hereunto annexed) a comparison is made for 

 quinquennial intervals of age, from the age 25 to the age 75 

 years, of the observed rates of mortality of the total male popu- 

 lation of England for the seventeen years 1838-1854, with the 

 corresponding rates exhibited at the same ages by the English 

 Life Table. In these ten quinquennial intervals of age the 

 proportional errors of observation vary from 6 per cent, to 12 

 per cent., and are alternately positive and negative. The mean 

 quinquennial error of observation is 9 per cent., either positive 



