Page:Popular Science Monthly Volume 19.djvu/503

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Considering the disadvantages under which he labored, it was a wonderful production. He had no record of the whole population, and only 6,193 births and 5,869 deaths of all ages from which to draw his deductions.

The form of the table has been substantially retained to the present day. It begins with 1,000 children, in the first year of life, of whom 145 die in the course of the year. At the beginning of the second year there are 855 living, of whom 66 die in the course of that year; and so the table continues until, at the age of 90, the last one of the original number will die. The probability of dying in any one year of life is readily ascertained. For instance, in the first year of life, 145 die out of 1,000. Therefore, the probability of dying is =·145. In the second year 66 die out of 855, which makes the probability =·077. That is to say, according to Halley's table, 14 per cent. of all newly-born children will die in the first year of life, and about 7 per cent. in the second year. Another interesting deduction pointed out by him is what a modern actuary has called the equation of life. It will be observed that, out of 1,000 at age 1, 499 will survive at 34, which indicates that the chances of dying or living to age 34 are about equal for a child at birth. It may be applied to any other age. At 19 the table shows 604 living, while at 54 there are 302; therefore, a youth at 19 has, to age 54, an equal chance of living or dying.

Whether Halley's table is a correct exposition of the mortality of the time it is difficult to say, since his data may have been insufficient; but the reasoning on which it was based and the conclusions drawn were strictly scientific.

But, while Halley's treatise must have been highly appreciated by mathematicians, the public at large seemed to have remained ignorant