That some Diseases are properly the Effects of the Influence of the
Heavenly Bodies, and that others do vary their Periods and Symptoms
according to the different Positions of one or other of those Luminous
Globes, is a very ancient and certain Observation. Upon this score
_Hippocrates_[18] advises his Son _Thessalus_ to the study of Geometry
and Numbers, because _the Knowledge of the Stars is of very great use in
Physick_[19]. And the earliest Histories of Epidemic Distempers,
particularly do all turn upon the alterations made in our Bodies by the
Heavens.
But when in later Times Medicine came to be accommodated to the
Reasonings of Philosophers; no body being able to account for the manner
of this Celestial Action, It was allowed no farther share in affecting
our Health, than what might be imputed to the changes in the manifest
Constitution of the Air, excepting perhaps something of Truth which
still remains disguised and blended with the Jargon of Judiciary
Astrology.
In order therefore to set this Matter in a little clearer light, I shall
in the first place shew, That the Sun and Moon regarding their Nearness
and Direction to the Earth only, besides the Effects of Heat, Moisture,
_&c._ thereby caused in our Atmosphere, must at certain times make some
Alterations in all Animal Bodies; then enumerate some Histories and
Observations of such Changes, and enquire of what Use such Thoughts as
these may be in the Practice of Physick.
It is a constant Observation of those who write the History of the
_Winds_, That the most Windy Seasons of the Year, are the Time about the
Vernal and Autumnal Equinox; for be the Air never so calm before or
after, we never fail of having Winds at that Juncture. Every body
likewise knows, that in the most quiet Weather we are sure of some
Breeze at Mid-day and Mid-night, as also at Full Sea, _i.e._ always
about the time the Sun or Moon arrive at the Meridian. Seamen and
Country People reckon upon This, and order their Affairs accordingly.
And the changes of the Weather as to Winds or Calms especially about the
New and Full Moon, are too well known to require any Authority to
confirm such Remarks. Those who desire a fuller account of these
Observations, may see it in _De Chales_'s Navigation, _Gassendus_'s
Natural Philosophy, and _J. Goad_, his _Astro-Meteoro-Logica_.
These things being Matters of Fact, and in a manner Regular and
Universal, it may very well seem strange that Philosophers have not been
more accurate in their Enquiries into the Reason of such Appearances.
True indeed it is, that the Origin of Winds is various and uncertain,
but however, so constant and uniform an Effect must undoubtedly be owing
to one necessary Cause.
It has bin, now a considerable time since, sufficiently made out, that
our Atmosphere is a thin Elastic Fluid, one part of which gravitates
upon another, and whose Pressure is communicated every way in a Sphere
to any given Part thereof. From hence it follows, That if by any
external Cause the Gravity of any one part shou'd be taken off or
diminished, that from all sides around this part, the more heavy Air
would rush in to restore the Equilibrium which must of necessity be
preserved in all Fluids. Now this violent running in of the heavier Air
would certainly produce a Wind, which is no more than a strong Motion of
the Air in some determined Direction. If therefore we can find any
outward Cause that would at these stated Seasons we have mentioned,
diminish the Weight or Pressure of the Atmosphere; we shall have the
genuine Reason of these Periodical Winds, and the necessary Consequences
thereof.
The Flux and Reflux of the Sea was a Phænomenon too visible, and too
much conducing to the Subsistance of Mankind, and all other Animals, to
be neglected by those who applyed themselves to the Study of Nature;
however all their Attempts to explain this Admirable Contrivance of
infinite Wisdom were unsuccessfull, till Sir _Isaac Newton_ reveal'd to
the World juster Principles, and by a truer Philosophy than was formerly
known, shew'd us how by the United or Divided Forces of the Sun and
Moon, which are encreased and lessened by several Circumstances, all the
Varieties of the Tides are to be accounted for. And since all the
Changes we have enumerated in the Atmosphere do fall out at the same
times when those happen in the Ocean; and likewise whereas both the
Waters of the Sea and the Air of our Earth, are Fluids subject, in a
great Measure, to the same Laws of Motion; it is plain, that the Rule of
our great Philosopher takes place here, _viz._ _That Natural Effects of
the same kind are owing to the same Causes_.[20]
What difference that known Property of the Air, which is not in Water,
makes in the Case, I shall shew anon; setting aside the Consideration of
that for the present; It is certain, That as the Sea is, so must our
Air, twice every 25 Hours, be rais'd upwards to a considerable height,
by the Attraction of the Moon coming to the Meridian; so that instead of
a _Spherical_, it must form it self into a _Spheroidal_, or _Oval_
Figure, whose longest Diameter being produced, would pass thro' the
Moon. That the like Raising must follow as often as the Sun is in the
Meridian of any Place, either above or below the Horizon. Moreover, That
this Elevation is _greatest_ upon the New and Full Moons, because both
Sun and Moon do then conspire in their Attraction; _least_ on the
Quarters, in that they then drawing different ways, 'tis only the
Difference of their Actions produces the Effect. Lastly, That this
Intumescence will be of a _middle degree_, at the time between the
Quarters, and New and Full Moon.
From the same Principles, The Motion upwards of the Air will be
strongest of all about the Equinoxes; the Equinoctial Line being over
that Circle of the Globe, which has the greatest Diameter, either of the
Luminaries when in that are nearer, and the Agitation of the Fluid
Spheroid revolving about a greater Circle, is greater; besides, the
Centrifugal Force (arising from the Diurnal Rotation) is there greatest
of all. This will still be more considerable about the New and Full
Moons happening at these times, for the Reasons just now mentioned. And
the least Attraction will be about the Quadratures of these Lunar
Months, because the Declination of the Moon from the Equator is then
greatest. The different distances of the Moon in her Perigæum and
Apogæum, are the Reason that these full changes fall out a little before
the Vernal, and after the Autumnal Equinox. Now the Inverse of all this
happens when the Luminaries are in the Solstitial Circles. Lastly, In
the same Parallel, when the Moon's Declination is towards the Elevated
Pole, the Attraction is strongest when the Moon is in that Places
Meridian, and weakest when she is in the Opposite Places Meridian: The
contrary happens in the Opposite Parallel; by reason of the Spheroidal
Figure of the Earth and its Atmosphere.
Whatever has been said on this Head, is no more that applying what Sir
_Isaac Newton_ has Demonstrated of the Sea to our Atmosphere; and it is
needless to shew how necessarily those Appearances, just now mentioned,
of _Winds_, at the Stated Times, _&c._ must happen hereupon. It will be
of more use to consider the Proportion of the Forces of the two
Luminaries upon the _Air_, to that which they have upon the Water of our
Globe; that it may the more plainly appear what Influence the
Alterations hereby made, must have upon the Animal Body.
Sir _Isaac Newton_ has demonstrated[21] That the Force of the Sun to
move the Sea, is to the Force of Gravity, as 1 to 12868200. Let that be
S. G :: 1. _n_. Hence, S = G/_n_.
And that the Force of the Moon to raise the Sea is to Gravity, as 1 to
2031821. Let this be