(S + L). C :: (G/_n_ + G/_s_). G/_e_ ::
(1/_n_ + 1/_s_). 1/_e_ ::
1. _sn_/((_s + n_) × _e_) :: 1. 6031.
The same Philosopher has taught us[22] that the Centrifugal force raises
the Water at the Equator above the Water at the Poles, to the height of
85200 Feet. Wherefore if that Force which is as 6031, raise the Ocean to
85200 Feet, the United forces of the Sun and Moon, which are as 1. will
raise the same to 14 Feet, for 85200/6031 = 14. _Proximé_.
Now we know that the more easily the Waters can obey the Attraction,
with the more Force are the Tides moved; but since, as Mr. _Halley_ has
determin'd it,[23] our Atmosphere is extended to 45 Miles, whereas the
middle depth of the Ocean is but about half a Mile; it is plain, that
the Air revolving in a Sphere about 100 times larger than that of the
Ocean, will have a proportionably greater Agitation.
Besides, Rocks, Shelves, and the inequality of Shoars are a great stop
to the Access and Recess of the Sea: But nothing repels the rising Air,
which is also of such thinness and fluidity, that it is easily driven,
and runs every way.
Nor ought we to omit, that it is the universal Law of Bodies Attracted,
that the Force of Attraction is reciprocally as the Squares of their
Distances; so that the Action of the Sun and Moon will be greater upon
the Air than upon the Water, upon the Account of its Nearness.
But the Consideration of the Elasticity is still of greater Moment here,
of which this is the nature, that it is reciprocally as the Pressure, so
that the incumbent Weight being diminished by the Attraction, the Air
underneath will upon this score be mightily expanded.
These and such like Causes will make the Tides in the Air to be much
greater than those of the Ocean; nor is it necessary to our purpose to
determine, by nice Calculations, their particular Forces; it is
sufficient to have proved that these Motions must both be Universal, and
also return at certain Intervals.
Now since the raising of the Water of the Ocean 14 Feet, produces
Torrents of such a prodigious Force, we may easily conceive what
Tempests of Winds (if not otherwise check'd) the Elevation of the Air
much higher (perhaps above a Mile) will necessarily cause. And there is
no doubt to be made, but that the same infinitely Wise Being, who
contrived the Flux and Reflux of the Sea, to secure that vast Collection
of Waters from Stagnation and Corruption (which would inevitably destroy
all the Animals and Vegetables on this Globe) has ordered this Ebb and
Flood of the Air of our Atmosphere, with the like good design, that is
to preserve (in Case all other Causes should fail, as they may, and at
times do in some Countries) the sweet Freshness, and brisk Temper of
this Fluid, so necessary to Life, and keep it, by a kind of continual
Circulation, from Deadness and Stinking.
This Reasoning is liable to only one Objection that I know of, and that
is this: That the Appearances we have mention'd cannot be owing to the
Causes now assigned; since by Calculation from them, the Mercury must at
New and Full Moon subside in the Barometer to a certain degree, which
yet we do not observe to happen.
In answer to which, (besides that there have been some Observations made
of the sinking of the Mercury at those times; and it may perhaps be the
fault of the Observers that these have not been reduced to any Rule) We
are to Consider, That altho' Winds and Alterations in the Pressure of
the Atmosphere, are the necessary consequents of the Lunar Attraction,
and true Causes of the different Rise of the Mercury in the Barometer;
yet these may be produced many others ways too, and therefore tho'
regularly the Mercury would always fall at the New and Full Moon, those
other Causes may be strong enough, even to raise it at those Seasons; in
as much as two contrary Winds, for instance, blowing towards the Place
of Observation, may accumulate the Air there, so as to increase both the
height and weight of the incumbent Cylinder; in like manner, the
Direction of two Winds may be such, as meeting at certain Angle they may
keep the Gravity of the Air in the middle place unaltered; and a
Thousand such Varieties there may be, by which the Regularity of
Appearances of this nature may be hindered. Now the other Springs, from
which such Changes in the Air may arise, are these.
1. Elastic Vapours forc'd from the Bowels of the Earth, by Subterraneous
Heats, and condensed by whatever cause in the Atmosphere.
2. A mixture of Effluvia of different qualities in the Air, may by
Rarefactions, Fermentations, _&c._ produce Winds and other Effects like
those resulting from the Combination of some Chymical Liquors; and that
such things happen, we are assured from the Nature of Thunder,
Lightning, and Meteors.
3. From the Eruptions of Vulcanoes and Earthquakes in distant Places,
Winds may be propagated to remoter Countries.
4. The divided or United Forces of the other Planets and of Comets, may
variously disturb the influence of the Sun and Moon, _&c._ We know that
there happen violent Tempests in the upper Regions of the Air, while we
below enjoy a Calm; and how many Ridges of Mountains there are on our
Globe, which interrupt and check the Propagation of the Winds; so that
it is no wonder that the Phænomena we have ascribed to the Action of the
Sun and Moon, are not always constant and uniform, and that every Effect
does not hereupon follow; which, were there no other Powers in Nature
able to alter the influence of this, might in a very regular and uniform
manner be expected from it.
These things being premised, it will not be difficult to shew (as was
proposed in the first Place) that these Changes in our Atmosphere at
High Water, New and Full Moon, the Æquinoxes, _&c._ must occasion some
Alterations in all Animal Bodies; and that from the following
Considerations.
1. All living Creatures require Air of a determined Gravity to perform
Respiration easily, and with Advantage; for it is by its weight that
this Fluid insinuates it self into the Cavity of the Breast and Lungs.
Now the Gravity, as we have proved, being lessened at these Seasons, a
smaller quantity only will insinuate it self, and this must be of
smaller force to comminute the Blood, and forward its Passage into the
left Ventricle of the Heart, whence a slower Circulation insues, and the
Secretion of Spirits is diminished.
2. This Effect will be the more sure, in that the Elasticity of the
Atmosphere is likewise diminished. Animals want Air as heavy so Elastic
to a certain degree; For as this is by its weight forced into the Cavity
of the _Thorax_ in Inspiration, so the Muscles of the _Abdomen_ press it
into the _Bronchi_ in Expiration, where the bending force being somewhat
taken off, and Springy Bodies when unbended, exerting their Power every
way, in Proportion to their Pressures, the Parts of the Air push against
all the sides of the _Vesiculæ_, and promote the Passage of the Blood.
We have a convincing Instance of all this, in those who go to the top of
high Mountains, for the Air is there so pure (as they call it) that is,
wants so much of its Gravity and Elasticity, that they Breathe with very
great difficulty.
3. All the Fluids in Animals have in them a mixture of Elastic _Aura_,
which when set at liberty, shews its Energy, and causes those
Fermentations we observe in the Blood and Spirits: Now when the Pressure
of the Atmosphere, upon the Surface of our Body is diminished, the
inward Air in the Vessels must necessarily be inabled to exert its
Force, in Proportion to the lessening the Gravity and Elasticity of the
outward; hereupon the Juices begin to ferment, change the Union and
Cohæsion of their Parts, break their Canals, _&c._
This is very plain in living Creatures put into the Receiver, exhausted
by the Air-Pump, which always swell as the Air is more and more drawn
out; their Lungs at the same time contracting themselves, and falling so
together as to be hardly discernible.[24]
E're we proceed to Matters of Fact, it may be worth the while to take
Notice, That Effects depending on such Causes as these, must of
necessity be most visible in Weak Bodies and Morbid Constitutions, when
other Circumstances concur to their taking Place. For this reason,
whatever Mischiefs do hence follow, cannot in the least disparage the
Wise Contrivance of Infinite Power in ordering these Tides of our
Atmosphere. The Author of Nature, we know, has made all things to the
greatest Advantage that could be, for the whole System of Animals on our
Globe, but it was impossible that such a disposition shou'd not in some
Cases be prejudicial to a Few. The Position and Distance of the Sun are
so adjusted, as to give in the most beneficial manner possible, Heat and
Light to the Earth; yet this notwithstanding, some Places may be too hot
for some weakly Bodies; some Autumns too sultry to agree with some
Animals, and some Winters too cold to be endured by some tender
Creatures: The whole however we must own, is most carefully provided
for. Besides, as most of these last mentioned Inconveniencies are by
easy shifts to be avoided; so there are such Powerful Checks put to this
Aereal Flux and Reflux, so many ways of abating the Damages accruing
from it now and then; that these are of no account in comparison of the
mighty Benefits hence arising, in which the Race of Mankind does
universally share.
[18] _Epist. ad Thessalum Filium._
[19] Ὀυκ ἐλαχίστον μέρος συμβάλλεται Ἀστρονομίη εἰς Ἰητρικήν. De Aere
Aquis & Locis.
[20] Newton, _Princip._ p. 402.
[21] _Princip. Lib._ 3. _Prop._ 36.
[22] _Ibid. Lib._ 3. _Prop._ 37.
[23] _Philos. Trans._ Nᵒ 181.
[24] _Esperienze dell' Academia del Cimento_, p.m. 113.