d,
And human bliss is ever insecure:
Know we what fortune yet remains behind?
Know we how long the present shall endure? WEST.

The writers of medicine and physiology have traced, with great
appearance of accuracy, the effects of time upon the human body, by
marking the various periods of the constitution, and the several stages
by which animal life makes its progress from infancy to decrepitude.
Though their observations have not enabled them to discover how manhood
may be accelerated, or old age retarded, yet surely, if they be
considered only as the amusements of curiosity, they are of equal
importance with conjectures on things more remote, with catalogues of
the fixed stars, and calculations of the bulk of planets.

It had been a task worthy of the moral philosophers to have considered
with equal care the climactericks of the mind; to have pointed out the
time at which every passion begins and ceases to predominate, and noted
the regular variations of desire, and the succession of one appetite to
another.

The periods of mental change are not to be stated with equal certainty;
our bodies grow up under the care of nature, and depend so little on our
own management, that something more than negligence is necessary to
discompose their structure, or impede their vigour. But our minds are
committed in a great measure first to the direction of others, and
afterwards of ourselves. It would be difficult to protract the weakness
of infancy beyond the usual time, but the mind may be very easily
hindered from its share of improvement, and the bulk and strength of
manhood must, without the assistance of education and instruction, be
informed only with the understanding of a child.

Yet, amidst all the disorder and inequality which variety of discipline,
example, conversation, and employment, produce in the intellectual
advances of different men, there is still discovered, by a vigilant
spectator, such a general and remote similitude, as may be expected in
the same common nature affected by external circumstances indefinitely
varied. We all enter the world in equal ignorance, gaze round about us
on the same objects, and have our first pains and pleasures, our first
hopes and fears, our first aversions and desires, from the same causes;
and though, as we proceed farther, life opens wider prospects to our
view, and accidental impulses determine us to different paths, yet as
every mind, however vigorous or abstracte