THE 
AMERICAN NATURALIST 
Vor. XXVII. Match, Igy: 315 
THE QUANTITY OF HUMAN LIFE. 
By J. Lawron WILLIAMS. 
Compared with periods of terrestrial history the duration of 
a human life even at the very longest is exceedingly brief. In 
our own time only a very few people ever live to see their 
hundredth birthday, and the average age is now calculated on 
the basis of elaborate statistics to fall between thirty-three 
and thirty-four years. 
It seems to bea prevalent opinion among unrefiecting peo- 
ple, that the quantity of an individual life is expressed by the 
number of days and years recorded on his or her tombstone. 
That such an opinion is erroneous will be rendered evident by 
a little consideration. First of all, in estimating the quantity 
of human life, we must possess some well defined conception 
of what we mean by the term life. This point settled, we can 
proceed with some degree of certainty in our calculation. Who- 
ever has devoted a little thought to the subject, cannot fail 
to be deeply impressed with the multitude and diversity of 
the factors which enter into the experiences of a life-time. 
There are the ever changing phenomena of the external world 
awakening and controlling the states of consciousness. There 
are the equally changeful individual activities perpetually 
giving rise to new internal changes. In other words, there is 
the physiological life utilizing the forces of nature, and mak- 
ing “ai subservient to the wants of the individual economy ; 
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