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identical. These differences, which represent the annual
differences in the population per cent. and range from 100 to
zero (at which latter point the births and deaths balance
each other), and from zero to —3.95, occupy a special column
on the extreme left of the table.
The first series of results (and these I shall quote at
length) are those which are deduced from a death-rate of .5
per cent. With a birth-rate of 100.5 par cent. and an annual
increase, therefore, of 100 per cent., the mean duration of life
is 7.6 years; with a birth-rate of 10.5 and an increase-rate of
10 the mean duration of life is 31.9; with a birth-rate of 8.5
and an increase-rate of 8 the mean duration of life is 36.81;
with a birth-rate of 5.5 and an increase-rate of 5 the mean
duration of life is 49.15; with a birth-rate of 5 and an
increase-rate of 4.5 the mean duration of life is 52.31; with
a birth-rate of 4.5 and an increase-rate of 4 the mean
duration of life is 56.02; with a birth-rate of 4 and an
increase-rate of 3.5 the mean duration of life (60.4; with a
birth-rate of 3.5 and an increase-rate of 3 the mean duration
of life is 65.8 ; with a birth-rate of 3 and an increase-rate of
2.5 the mean duration of life is 72.56 ; with a birth-rate of
2.5 and an increase-rate of 2 the mean duration of life is
81.27 ; with a birth-rate of 2 and an increase-rate of 1.5 the
mean duration of life is 93.1; with a birth-rate of 1.5 and an
increase rate of 1 the mean duration of life is 110.4; with a
birth-rate of 1 and an increase rate of .5 the mean duration
of life is 138.98; and with a birth-rate of .5 and a consequent
stationary condition of the population the mean duration of
life is 200. Lastly, with a birth-rate of .05 per cent., or of
only 5 in 10,000, and a consequent annual diminution of the
population by .45 per cent., or by 45 in 10,000, the mean
duration of life is 510.54 years.