a reactive tendency promoted towards noon under the solar influence, and
again towards evening this reaction is repressed by the sedative effect
of the evening cold; and this sedative effect is at its maximum at
midnight. Hence those who sit up late feel unusually chilly and
depressed towards midnight, partly owing to exhaustion from want of
sleep, but chiefly from the total absence of solar influence in the
atmospherical temperature. In regular habits this sedative effect is
never thoroughly experienced; for before midnight, the constitution,
enveloped in warm blankets, has experienced the reaction arising from
the accumulation of heat in bed. Whence the common remark, that one
hour's sleep before midnight is worth three after that hour, is actually
true to a certain extent. By early retirement to rest, the sedative
effect on the constitution, to an extent such as to disturb the
functions, is escaped.

If we connect these two influences, the annual and diurnal successions
of cold and heat, in their joint effect, we find, that about, or a
little after the summer solstice, the influence of the sun being at its
maximum, the nervous sensibility, heat, circulating excitement, and
cutaneous secretions of the body, are also at their maximum. The
temperature of the day and night differ so little, that the sedative
effects of evening and morning are not sufficient to restore the frame
by soothing the sensibilities, overexcited and irritable from the
previous warmth. Whence the languor and irritability felt in summer,
when the heat is long continued, and the nights are spent in
restlessness and anxious oppression. Exhaustion and relaxation of the
frame are the consequence.

As the autumnal equinox verges on, the mornings and evenings get cooler
in relation to the mid-day heat; and about the equinox, the difference