frequency about the equinoxes.

16. There are numerous instances of the effect of the lunations upon the
periods of insanity, whence the name of lunatic has been given to those
afflicted with this disease.

IV. The critical days, in which fevers are supposed to terminate, have
employed the attention of medical philosophers from the days of Hippocrates
to the present time. In whatever part of a lunation a fever commences,
which owes either its whole cause to solar and lunar influence, or to this
in conjunction with other causes; it would seem, that the effect would be
the greatest at the full and new moon, as the tides rise highest at those
times, and would be the least at the quadratures; thus if a fever-fit
should commence at the new or full moon, occasioned by the solar and lunar
attraction diminishing some chemical affinity of the particles of blood,
and thence decreasing their stimulus on our sanguiferous system, as
mentioned in Sect. XXXII. 6. this effect will daily decrease for the first
seven days, and will then increase till about the fourteenth day, and will
again decrease till about the twenty-first day, and increase again till the
end of the lunation. If a fever-fit from the above cause should commence on
the seventh day after either lunation, the reverse of the above
circumstances would happen. Now it is probable, that those fevers, whose
crisis or terminations are influenced by lunations, may begin at one or
other of the above times, namely at the changes or quadratures; though
sufficient observations have not been made to ascertain this circumstance.
Hence I conclude, that the small-pox and measles have their critical days,
not governed by the times required for certain chemical changes in the
blood, which affect or alter the stimulus of the contagious matter, but
from the daily increasing or decreasing effect of this lunar link of
catenation, as explained in Section XVII. 3. 3. And as other fevers
terminate most frequently about the seventh, fourteenth, twenty-first, or
about the end of four weeks, when no medical assistance has disturbed their
periods, I conclude, that these crises, or terminations, are governed by
periods of the lunations; though we are still ignorant of their manner of
operation.

In the distinct small-pox the vestiges of lunation are very apparent, after
inoculation a quarter of a lunation precedes the commencement of the fever,
another quarter terminates with the complete eruption