y yonder blessed moon I swear,
That tips with silver all these fruit-tree tops--
_Jul_. Oh, swear not by the moon, the inconstant moon,
That monthly changes in her circled orb,
Lest that thy love prove likewise variable." [419]

Upon the physiological influence of the lunar rays in the generation
or aggravation of disease, we have but little to add to what has been
already written. It is a topic for a special treatise, and properly
belongs to those medical experts whose research and practice in this
particular branch of physics qualify them to speak with plenary
authority. Besides, it has been so wisely handled by Dr. Forbes
Winslow, in his admirable monograph on _Light_, that inquirers
cannot follow a safer guide than his little book affords. Dr. Winslow
accounts for the theory of planetary influence partly by the action of
the moon in producing the tides. He says: "Astronomers having
admitted that the moon was capable of producing this physical
effect upon the waters of the ocean, it was not altogether unnatural
that the notion should become not only a generally received but a
popular one, that the ebb and flow of the tides had a material
influence over the bodily functions. The Spaniards imagine that all
who die of chronic diseases breathe their last during the ebb.
Southey says, that amongst the wonders of the isles and city of
Cadiz, which the historian of that city, Suares de Salazar,
enumerates, one is, according to p. Labat, that the sick never die
there while the tide is rising or at its height, but always during the
ebb. He restricts the notion to the isle of Leon, but implies that the
effect was there believed to take place in diseases of all kinds, acute
as well as chronic. 'Him fever,' says the negro in the West Indies,
'shall go when the water come low; him always come not when the
tide high.' The popular notion amongst the negroes appears to be
that the ebb and flow of the tides are caused by a '_fever of the
sea_,' which rages for six hours, and then intermits for as many
more." [420] Dr. Winslow then subjoins a long list of learned
authorities, several of whose writings he subjects to a brief analysis.
He disapproves of the presumption that the subject is altogether
visionary and utopian; and affirms that it has not always been
pursued by competent observers. Periodicity is noted as an
important symptom in disease; a feature in febrile disturbance which
the present w