Chapter LXXXVI: Section 52: , Note (a), corrected; the circular Distance from

the Eye, above the Clouds, was 102 Miles, 1 Quarter, 320 Yards: while _that_ above the Earth, seen from the same elevated Situation, (supposing the Day to have been +clear+ for such a View,) was 102 Miles, 1 Quarter, 307 Yards: whose Difference is only 13 Yards: that is, the _Distance_ above the Clouds to the _nebulous_ Horizon, was _rather_ more extensive, than _that_ above the Earth to the _terrestrial_ Horizon.

It may not, to some Readers, be deemed either unentertaining, or foreign to the Subject; if the Distance of the _Prospect_ from the Balloon at its greatest _barometric_ Altitude, viz. 2332 Yards, or a Mile and Half within 33 Yards, be compared with the Distance which may be seen from the _Summit_ of the principal Mountains in different Parts of the Globe.

1. Cotopàzy, a Mountain in the Province of Quito, in America, and under the equinoctial Line, is _said_ by Ullòa (Vol. 1. Page 422) to be 3126 Toizes or Fathom, i.e. 6252 Yards, or 3 Miles and a Half and 92 Yards in Height.

2. White Mountain, called by the French Mount Blanc, near Geneva, is considered by Sir G. Shuckburgh (Phil. Trans. Vol. 67, Part 2d, Page 598, for the Year 1777) as the highest Land in Europe, Asia, or Africa (known to Europeans) and calculated by him at 5220 Yards, or 3 Miles within 60 Yards above the Level of the Mediterranean Sea.

Mons. Bourit just returned from his last Tour, see his “Description de Glacieres” in 1773, makes the White Mountain but 5102 Yards in Height, (which is 30 Yards lower than Teneriffe) including the 410 Yards for the Level of the Lake of Geneva above the Mediterranean.

3. The Peak of Teneriffe in the Canary Islands, which, _in approaching towards it_, Authors agree, may be seen at the Distance of 120 Miles at Sea, if the Weather is clear; (Modern History, Vol. 14th, Page 451;) and, in _returning from it_, is discoverable at the Distance of 150 Miles, according to Glas’s History of the Canaries (Page 234);—has been estimated by Dr. Heberden in Madeira (Guide to the Lakes, Page 187) at 5132 Yards, or 3 Miles within 148 Yards.

Glas remarks farther, that in sailing from Teneriffe, the Peak, at the Distance of 150 Miles is very little darker than the _azure_ Sky, on Account of the great Quantity of Vapour intercepted between the Eye and the Mountain: and _not_ because it ceased to be an Object too small for the Sight; or was in Fact, below the Horizon, and only raised by Refraction of the Vapour.

With Respect to the Peak of St. George, situated in the Island called _Pico_, one of the Azòres; the Writer of this Account asserts, from the Mouth of an able and experienced Officer in his +Majesty’s+ _Navy_, who, during the last War, cruized some Weeks off those Islands; that the latter has frequently observed the Peak, at the Distance of 120 Miles, and coud then distinguish a _third_ Part of its Height _down_ the Mountain. Section 126, Note (_a_), see also [46] below.

4. Etna is 3877 Yards above the Mediterranean: (according to Brydone’s Tour throu’ Sicily and Malta, Vol. 1. Page 211) or 2 Miles and 357 Yards.

5. Blue Ridge, the highest Mountain in the Island of Jamaica, is, according to Dr. Clark, who measured it in November last, 3080 Yards, or 1 Mile and three Quarters, above the Level of the Ocean.

The +distance+ to be +seen+ is considered as terminating the Radius of a Circle, whose Center is the +eye+ of the Observer, on _each_ Mountain.

_Height of the Mountains._ +distance+ _to be_ +seen+
_from them in Miles_.

_Cotopàzy_ 3 Miles and a Half and }
92 Yards, (for the Process, } 167½ and 405
see Section 52, Note (_a_)). } Yards.

_White Mountain_ 3 Miles within } 153¼ and 13
60 Yards. } Yards.

_Peak of Teneriffe_ 3 Miles within } 152 within 72
148 Yards. } Yards.

_Mount Etna_ 2 Miles and 357 } 132 and 127
Yards. } Yards.

_Blue Ridge_ 1 Mile and 3 Quarters. } 117¾ and 30
} Yards.

_Balloon_ 1 Mile and half within } 102¼ and 307
33 Yards. } Yards.

As it is well known that Objects of the _greatest_ Magnitude appear but as +blue air+ at even a _less_ Distance than 100 Miles; to which add the Difficulty of Journies, and Ascent to the Summit of these astonishing Mounds of Earth; and all this for the Sake, not of a complete +down prospect+, subject to _a perpetual Variety_, but merely an _imperfect Side-View_: the +pleasure+ and +ease+ of attaining still _more_ stupendous Heights at _any_ Place and Time, by Means of the +balloon+, are strikingly in Favor of that Invention. And, notwithstanding the confessed Merit of Dr. Black’s Project with the _Farciminàlis_ of a Calf, and Mr. Cavallo’s Soap Bubbles with inflammable Air; (see his History of Aerostation, Page 34;) if the Emperor had been alive who offered a Reward for the Invention of a _NEW PLEASURE_; the _first_ Prize had been due to the Brothers Montgolfier, and a _second_ to the Brothers Roberts.

[46] As therefore it may be supposed that the Peak of St. George, in _receding_ from it, woud _vanish_ at the Distance of 150 Miles; its Height may _easily_ be ascertained geometrically thus:

See the Figure annexed.

Let M be the Summit of the Mountain: and let the Line M T drawn to the Circumference of the Circle at T, be the _evanescent_ Distance of the Mountain in the Horizon, viz. 150 Miles.

Join T C, viz. a Line drawn from the _Tangent_ to the Center of the Circle, which Line will therefore represent the Semidiameter of the _Earth_, viz. 3958 Miles, according to Newton.

Draw a Line from C to M, which will pass throu’ some Point of the Circumference as H, the Base of the Mountain.

Then, in the Triangle M T C, as the Angle at T is a right Angle (Euclid’s Elements, Book 3, Proposition 18;) and the Sides M T, and T C, containing the right Angle, are _known_; the _third_ Side C M is readily found: (being a Corollary to the 47th Prop. 1st Book Euclid:) viz. having the two Sides of a right Angle Triangle given to find the _third_. Therefore

RULE.

Multiply the Sides containing the right Angle, each into itself: viz. 150 and 3958: add the Products into one Sum: from which extract the _square Root_; _equal_ to the Length in Miles, of the _third_ Side required.

From the _third_ Side, subtract that Part, viz. C H, which is equal to the Semidiameter T C already found: and the Remainder H M is the _Height of the Mountain_.

Thus: 150 Miles. 3958 Miles in the Semidiameter of
150 3958 the Earth.
——— ————
7500 31664
15 19790
————— 35622
22500 11874
Square of the ————————
greatest visible 15665764 Square of the Semidiameter
Distance. add 22500 of the Earth.
————————
Extract the sq. Root, 15688264 ( 3960.84 Square Root.
9 3958 subtract.
—— ————
69) 668 Rem. 2.84 Answer in Miles.
621
———
786) 478.2
471 6
—————
79208) 6664.00 continued to 2 Decimals.
6336 64
———————
792164) 32736.00 ditto.
31686 56
————————
104944

To find the .84 Part of a Mile; multiply
1760 Yards in a Mile,
Decimal Parts of a Mile to be reduced .84 into Yards.
————
7040
14080
——————
1760)1478.40(0
Subtract 1478
————
282

Answer: the Height of the Mountain is 2 Miles 282 Yards.

[47] Rays flowing from the Sun seem to be +red orange+ or +yellow+, according to the Quantity of Vapours floating in the Atmosphere, which absorbs the most refrangible ones: and the fewer the Vapours the more does the Sun’s Light approach to a perfect and intense +white+, according to the Doctrine of Newton: which seems to receive Confirmation from the Purity of the Solar Light, when seen _above Clouds_ and _Vapours_, in the Balloon: where the Sun shines not so much with a _golden_ as with a _sparkling_ +silver+ Light.

[48] +Sounds immediately under+ the Balloon, seemed, as if originated _near_ the Ear, and _louder_ than they would have been heard, at the Distance of some Yards _only_, when on a Level with themselves: augmenting rather than decreasing, during the _Ascent_ of the Balloon, till it arrived to a Height indicated by the Barometer at 27 Inches. Presently afterwards, the Balloon still rising; the Sounds _died away_: much sooner indeed than was expected.

The like was observed in _descending_ from a State of perfect Tranquillity and Silence: _Sounds_ from _below_, when about the same Height, _suddenly rushing_ on the Ear.

It must be considered that by _this_ Time, the +shadows+ were much encreased; tho’ at half past II, they were _more_ than double in Length to the Height of each Object.

The Trees woud therefore spread a +shade+ _across_ the Road.

The +tops+ of the _Houses_ likewise, being Part of them in the Shade; and either _thatched_ with Straw, or covered with Slates of a _dusky_ Hue; woud prevent their _throwing off_ any _striking_ Colour.

Possibly the _Encrease_ of Shade _alone_, might give the Face of the Country _below_, a _dark-green_ Cast.

It is certain that the Height of the Balloon must have been very great, to prevent the Sight of public and _Turnpike-Roads_, _above_ which it _frequently_ passed, and which had been +plainly+ seen _before_ the _Re-ascent_.

For suppose the Road but 5 Yards wide, which is less than the Truth; if it be allowed that an Object may be distinguished by a _sharp_-sighted Person, when its _Distance_ from the Eye does not _exceed_ 5156 Times the Diameter of the Object; i.e. when the Object does not subtend a _less_ Angle at the Eye than _30 Seconds_ of a Circle, (Smith’s Optics, Article 97) which is the _smallest_ visible Point, and equal to the 8000th Part of an Inch on the _Retina_;—by multiplying 5 Yards, viz. the Diameter of the public Road, into 5156 (or, in round Numbers, into 5000) Times its Distance from the Eye in the Balloon; the Product is 25000 Yards: which Product being divided by 1760, the Number of Yards in a Mile, amounts to 14 Miles, and 360 Yards.

Supposing farther, that a _common_ Eye can _only_ see an Object at _half_ that Distance; the Height woud _then_ be 7 Miles.

The _Improbability_, therefore, (on Account of the _Warmth_ of the Air at that Height, viz. 60°;) of having _soared_ to so great an Altitude, seems to point out, that the +shadows+ must have contributed a _principal_ Share, in preventing a Sight of the public and _Turnpike_ Roads.

[49] The +magnitude+ of an Object _decreases_, as the +squares+ of its Distance from the Eye _increase_.

At whatever Distance, for Example, the Eye can see any Object clearly; as at the Distance of a Foot, or a Yard, if the Object be removed to _twice_ that Distance; it will appear 4 Times smaller than it did before: 2 multiplied into 2, equals 4, which is the Square of 2: in the same Manner, if the Object be removed to thrice the Distance from the Eye, it will appear 9 Times as small, as at the first Distance: for 3 into 3 gives 9, the Square of 3: and so of any farther Distance.

[50] See “Berkeley’s New Theory of Vision, Section 67.”

[51] Dr. Smith having Recourse to _intervening Objects_; the Writer cannot assent to the Validity of his Argument, illustrated by a well-known Figure, to solve the Appearance of the _horizontal Moon_. See “Priestley’s History of Light and Colours, Page 712.”

[52] Phil. Trans. for 1785, Part 1, Page 287.

[53] Cavallo’s Treatise on Air, Page 576. Vitriolic Acid Air, Alkaline Air, and other elastic Fluids, are instantly +absorbed+ by _Water_; (Page 673.) Inflammable Air, and fixed Air, are likewise +absorbed+ by +water+. (Page 434).

[54] Nam fit, ut interdum tanquam demissâ Columnâ
In Mare de Cœlo descendat.—Lucr. L. 6. V. 425.
_Una_ Eurus Notusque ruunt, creberque Procellis
Africus. Also
Omnia Ventorum _concurrere_ Prælia vidi. +Virgil.+

[55] Franklin’s Account of Whirlwinds and Waterspouts, in his Miscellaneous Tracts. Lowthorp’s Abridgement of Phil. Trans. Vol. 2. Page 103. Varenius Geogr. Gen. C. 21, Pag. 265. A clear Account of the Effects of a +depression+ is to be met with in “the History of Jamaica, in 3 vols. vol. 3. Page 800, on _Trade and Land Winds_.”

[56] Mons. Maupertius has found, that the extreme Cold at Tornea, in the northern Regions beyond the Artic Circle, came directly from _above_: see “La Figure de la Terre,” Page 59. Il semble que le vent souffle—de tous Côtés à la Fois; et il lance la _Neige_ avec une telle Impetuosité, qu’en un Moment tous les Chemins font perdus. “It seems that the Wind blows from all Points of the Compass at once,” &c.

[57] The Doctrine of smokey Chimnies distinctly treated of under the Article +smoke+, in the Encyclopædia Britannica, may receive some Improvement, from Circumstances which ascertain the sudden Descent, Elevation, and quick Depression of _Columns_ or rather _Torrents_ of Air, viz. by widening the Tubes, and covering their Tops.

[58] It is thought more _candid_, and will to _many_ be more _satisfactory_; to make occasional References to different Authors who have treated distinctly on a Subject, and leave the Reader to draw his own Conclusions by applying to their _express_ Words;—than, either to insert abundant Quotations; or _weave_ their Thoughts into the _Texture_ of the Work: which must encrease its Bulk, without producing any Thing either new or instructive.

[59] Once, particularly, in the Month of January, at Lausanne: Farenheit’s Thermometer at 7 only: the Country covered with Snow; and a North Wind beating +violently+ on the Lake, which continued liquid without Ice: owing, perhaps, in _Part_, to subterranean Heat, and Exhalations.

[60] The Depression and Reverberation of the Wind near Rivers, and its Descent from Mountains, _a Point to be discussed_, may furnish a Hint and Reason, why Rain falls more in one Place, than in another not far distant: and why in the same Place it falls in different Quantities, at different Heights, irregularly.

[61] Cavallo’s Treatise on Air, Page 446.——

[62] 442.——

[63] 441.——

[64] 442.

[65] It is _light_ in Consequence of its _Warmth_, when compared with the _cooler condensed Air_ above it.

[66] In the same Manner that Curls and Streams of Air _descended_ into the Bason over the rising _Steam_, and interrupted the Regularity of _its_ Elevation; in the _larger_ Towns, during Winter (_the Weather being moderate_) the Pressure of Air on all Sides, from without, produces a constant Breeze towards the Center of the Town: as may be discovered, not only by the Smoke in its Deviation from the Perpendicular, as it issues from the Chimneys; but by all who are inclined to make the Trial; for, on leaving the Town, they will _meet_ the Breeze.

In calm Weather, during Summer, the contrary Event happens: but more particularly in _hot_ Climates. For the Country being hotter than the Town; a _Depression_ of the Atmosphere takes Place, and scatters the Smoke on all Sides round the Town.

The Cities in Italy, and other hot Climates, on Account of the Buildings, and _desirable_ Narrowness of the Streets, form _one_ contiguous _Shelter_, _Arbor_, or grand _Parasol_: For which Reason, the Nobility leave the Country, and reside in the Towns during Summer: there finding a Coolness and Refreshment unknown on the _scorching_ Plains.

A _Reception_ and _Dispersion_ of Air takes Place; _as will presently be mentioned_.

The same ocular Proof and Process in the Evaporation of Steam, accounts at once, for a curious Phenomenon constantly observable on all Waters; viz. _a narrow_ +smooth+ _irregular Surface of considerable Length, nearly in the Direction of the Wind, yet unaffected by it_: all which is probably nothing more than _rising_ Volumes of _elastic invisible_ Steam; _resisting_ the _two_ nearest _descending Waves_ of +air+; and preventing them from approaching the _Surface_ of Water, over which the Steam is compressed; and _there_ producing a _temporary_ +calm+.

[67] Phil. Trans. for 1777, Page 470. Thibet in Lat. 31, _cold_ with Snow and Frost.

See Ullòa’s Voyage to South-America, Book 6, Chapter 7; where he describes the snowy Mountains, under the Equator.

As the Weather, near the Equinoctial, is more regular, its Changes closely following those of the Moon; and also the Winds and Hurricanes more violent; the Truth of the foregoing Theory will receive the strongest Confirmation by tracing the Effects of +depressing torrents of air+, in the Island of Jamaica, extracted from the Author already mentioned.

“The cool Vapour _rushes_ from the Mountains towards the hot dry Air, which hovers over the Savannahs or Vallies.

The Rain falls heaviest in the Mountains. Vol. 3, Page 600.

The _Land-Wind_ after Rain, proceeds from that Quarter whence the Rain has fallen _heaviest_; and seems to _rush_ from above.

In Spain and North-America, the Wind _rushes down_. Page 601.

When the _Land_ is _most_ heated, the Sea-Breeze blows almost _all_ Night. Page 602.

The Barometer subsides from 1 Inch to 1½ _at_ the full Moon, or just _after_ it.

Wind blows from the Mountains all round the Island: and still a Sea-Breeze over the Mountains: to the Low-Lands, none, 604.

(In Jamaica likewise the Wind blows off the Island _every way_ at once, so that no Ship can any where come in by Night, or go out but early in the Morning, before the Sea-Breeze sets in. See Abr. Phil. Tr. Vol. 3, P. 548.)

_Mountain Air rushes down in a continual Current to every Part of the Coast, the Stream descending incessantly throu’ the Night: while heavy cold Air descends to the Mountain Tops_, 604.

With a _West_ Wind below there is an _East Scud above_, 605.

_Mountains_ +cloudy+, _low Lands_ +sunny+. 606.

In +all+ _the River-Courses of Jamaica, there is a sensible Current of Air. Rain never comes without some Wind: and the Showers almost invariably follow the very Meanders of the larger Rivers_, 608.

Rain always cools: the Thermometer falling, after a Shower, from 6 to 8 Degrees, 610.

(And Iron rusts least in rainy Weather: [the Air being then +driest+,] descending from the _upper_ Regions. Abr. Ph. Tr. V. 3, P. 546.)”

It is said also that “in Jamaica the Clouds gather, and _shape_ according to the Mountains: so that _old Seamen_ will tell you each _Island_ towards Evening, by the _Shape_ of the Cloud _over_ it.”

The Sea-Breeze, being counterpoised by _Descent_ of the _etherial Air_, produces a +calm+.

The same Author likewise says, that “the Clouds begin to gather about 2 or 3 o’Clock in the Afternoon _at the Mountains_, and do not _embody_ first in the Air, and after settle there, but _settle_ first and _embody_ there: the rest of the Sky being clear till _Sun-set_. So that they do not pass _near_ the Earth in a _Body_, and only _stop_ where they meet with Parts of the Earth elevated _above the rest_; but +precipitate+ _from a very great Height_, and in Particles of an _exceeding rarified Nature_; _so as not to obscure the Air or Sky at all_: that great Variety of beautiful Colours in the Canopy of Heaven being raised to a much greater Distance [he means Height] in Jamaica than it is here.” Abr. Ph. Tr. V. 3, P. 557.

(Prognostics of Weather, at certain Periods of the Moon, are mentioned by Captain Langford. Lowthorp’s Abr. Phil. Trans. Vol. 2, Page 105.)

[68] The Depression of a _Torrent_ of Air in the Form of an hyperbolic Solid, _contracting_ as it _descends_ to the Earth, in Proportion as its _Density_ encreases; may furnish a Hint towards the Solution of a Difficulty how to account for the Augmentation of vesiculous Vapours into large solid Drops, frequent during _Summer_-Showers.

[69] Mons. Saussure’s valuable “Essais sur L’Hygrometrie,” throw new Light on the Doctrine of Rarefaction and Condensation not unfavourable to the Hypothesis here advanced. Page 260.

[70] Ice, when exposed to marine acid Air, is dissolved by it, as fast as if it touched a red hot Iron. See Cavallo’s Treatise on Air, Page 727. Also Priestley’s Experiments and Observations, Vol. 1, Page 148.

[71] “The +water+ remains +transparent+ or colourless, tho’ saturated with marine acid Air, and by a very gentle Degree of Heat, the Gass may be again expelled from it, as it is expelled from Spirit of Salt.”

This Observation is applicable to the Transparency of Vapours, in the Air, tho’ mixed with the marine Acid exhaled from the Sea: for when the acid or Sea Air is mixed with Alkaline or Land Air, they instantly _combine_; lose their Elasticity, and form a _white_ visible Substance or _Cloud_. Cavallo, Page 728. Priestley’s Exp. and Obs. Vol. 2, Page 293.

[72] On the Descent of Air in _Thunder-Gusts_, see “Chalmer’s Account of the Weather in South-Carolina, Vol. 1, Page 1, to 39.”

[73] “Historia Ventorum, Pag. 54, Art. 34.”

[74] Book V. Chapter 2d.

[75] Vol. 1. Page 184.

[76] Page 195.

[77] History of the Canary Isles, Page 252.

[78] As the superior Clouds, during the Balloon Excursion, did not much exceed the Height of 1000 Yards; supposing then the Clouds at an equal Height above the Sea, near Teneriffe; one ought to conclude, either, that the Peak was not so high as Glas represents it; or, that the Level of the Clouds was less than half the Height of the Mountain.

[79] See “Royal Astronomer, by R. Heath, Page 321, on _Trade Winds and Monsoons_.”

[80] One Pound of Nitre only, producing by mere Heat, 6 cubic Feet of Air. “Cavallo, Page 332, and 811, Experiments on Gun-Powder.”

[81] “See Recherches surles Modifications de l’Atmosphere. No. 715.” Ph. Trans. Part 2, for 1777. Col. Roy’s Experiments, Sect. 2d, Page 689, 744, 753, 764.

[82] The different Phenomena of the _Aurora Borealis_ may be owing to the Ascent and Motion of the Apogay, in the _middle_ Region, over the Stratum of Eknèfiai or _Ground_-Winds.

The Effects of _Tides in the Air yet to be_ mentioned, must not, however, be wholly excluded.

The Aurora Borealis is seen in _Spring_, _Autumn_, and _Winter_: sometimes _culminating_, sometimes moving in _Streams_ and _Waves_ in the _superior_ Regions of the Atmosphere: when culminating; as if rising out of Clouds in the North.

This Appearance may be owing to warm moist Air perpetually generating between the Tropics, and rolling over the cold _dry_ Stratum of Eknèfiai Winds, which cut off its Communication with the Earth: till accumulating over the Poles, it enlightens the Atmosphere, converting a six _Month’s Night_ into Day; and returns to the Surface silently: or in Lightning, whenever it is communicated to the Earth, throu’ _Vapour descending_ by its own specific Gravity; or along with _depressing_ Torrents of Air, known to be accompanied by frequent +flashes+.

When the Vapour is _condensed_ in its Descent, by passing throu’ a Stratum of the Eknèfiai Winds; it becomes _overcharged_ with the electric Matter, _surrounding_ and _adhering_ to it; and deposits the Overplus in Lightning, on its Approach to _other_ Clouds, or to the _Earth_.

It is visible in the Form of a Vapour, when the Vapour to which it adheres, becomes overcharged with electric Matter, by Descent into a _cool_ Eknèfiai Stratum below: there forming a luminous and transparent Atmosphere: the Particles of Light and Vapour being repelled to great Distances from each other at so _rare_ a Height.

It culminates above the Vapour, because less heavy than the circumambient Air: and may be subject to the Attraction of other Planets.

The Aurora Borealis is also seen to issue in Streams and Waves of Light, with inexpressible Velocity, on its Return to the South, in a lower Stratum, as it _passes throu’_ Interstices, between the Vesicles of warm Vapour, raised and dispersed by the turbulent Apogay Winds, in the middle Region.

During Summer, the middle Region becomes blended with the lower, throu’ Defect of Cold: and the electric Matter is supposed to be communicated to the Earth, silently, and continually; but by Lightning, when a lower and colder Atmosphere condenses and overcharges the Vapour, and cuts off the Communication.

It cannot be seen but in escaping from Vesicle to Vesicle: nor, during Summer, after Sunset, on Account of the Twilight.

[83] Air is not unfit for Respiration, by having lost its _vital_ Principle, but because it has imbibed _Floguiston_, which cannot _easily_ be separated from it, but by Agitation in Water. Cavallo, on Air, Pages 479, 670.

[84] For if Moisture be one Cause, which keeps the Particles of Air at greater Distances from each other; this Cause decreases at _great_ Altitudes.

If also the _Elasticity_ decreases in Proportion, not only to the Height, but the Driness; its Particles must, on both Accounts, approach each other, at great Altitudes: tho’, from the Altitude only; they woud separate according to the Rule, viz. that the Rarity of the Air is proportionable to the Relaxation of the Force compressing it.

So that at the Height of 8 or 10 Miles, a Quantity of Air taken from the Surface of the Earth, woud occupy 6 Times its former Space: supposing the Air both below and above to be of the _same Kind_, as well as of the _same mean_ Temperature of 55, on the Thermometer. See “Martin’s Philosophical Grammar, Page 178.”

[85] Chalmer describing a Whirlwind, which is a _Storm_ of +collection+ and _Ascent_ of +hot+ Air, &c. by Rarefaction, says, “as the Wind ceased, presently after the Whirlwind passed, the +branches+ and Leaves of various Sorts of Trees, which had been carried into the Air, continued to +fall+ for +half an hour+; and, in their Descent, appeared like Flocks of Birds of different Sizes.”

This Circumstance proves that Columns of +hot+ Air must have been raised in a Body, in Succession, to so considerable a Height, that _Branches_ of Trees carried up by them, took _half an Hour_ in falling.

[86] It may be from this Principle, that in the East, Liquids are kept _cool_ by being hung in the Shade, in the _open_ Air, suspended in _wet Cloths_: there being a continual Breeze and Succession of +cool dry+ _Spunges_ (as it were) of Air, in Contact with the _wetted_ Cloths, whose Moisture will thus be more quickly evaporated.

[87] Historia Ventorum, Pag. 48, Art. 33.

[88] “Cum enim (Venti) Choreas ducant, Ordinem Saltationis nosse jucundum fuerit. Art. 18.”

[89] On the Action of the Sun and Moon over Animal Bodies, by Dr. Mead, Miscell. Cur. Vol. 1. P. 372, 373.

[90] For these Observations see Gassendus’s Natural Philosophy. De Chales’s Navigator. And Astro-Meteoro-Logica, per J. Goad.

[91] See Maclaurin’s Newton, Page 376.

[92] Air at a Medium is 800 Times _rarer_ than Water: so that if 800 Times the Quantity of Air _naturally_ contained in a Vessel whose Dimensions are those of a cubic Foot, were pressed into it by a Syringe or _Condenser_, the Air woud differ nothing from Water in Density.

[93] See Wilson on Climate, Chap. 15. Pages 46, 54.

[94] 55.

[95] By reducing 10 Feet 6 Inches, and 6 Feet 7 Inches, into Inches, and dividing by common Divisors, as 3 and 2; it is found that 10 Feet 6 Inches, will be to 6 Feet 7 Inches, as 3 to 2 nearly: that is, as 15 Miles to 10 Miles.

[96] White’s Ephèmeris, Page 38, for the Speculum Phenomenorum, or Mirror of the Heavens.

[97] See the Book which gives an Account of Walker’s Eidouranion.

The _intelligent_ Reader will easily distinguish the Effects, attributed to the Planets, viz. their mutual Attractions, owing to natural Causes only;—from the futile Ravings of judicial Astrology.

[98] See London Chronicle, 26th July, 1785.

[99] To find the Direction of an upper Current, without the Inconvenience of rising above the Level which the Aironaut has fixed on.

This the Abbé Bertholon has hinted at, by Means of a smaller Balloon.

The Dimensions of which, must however be so large; that, allowing for the Evaporation of Gass, it will _just_ rise with the Weight of a Quantity of Cord, a Mile and half, for Instance, in Length: and have sufficient Room left within, to admit of the Expansion of Gass without Rupture.

The Pioneer-Balloon may be taken up, _empty_, and filled with Gass necessarily escaping from +the mouth+ of the _great Balloon_, when stationary: and may be sent up with a Cord, fastened to the Center above the Car of the _great Balloon_, to reconnoitre the _superior_ Currents: or it may be only filled _in Part_; and made to _descend_, and _discover_ the _lower_ Currents.

See “Des Avantages de Ballons, &c. Page 72.”

[100] As the _Heights_ of the Atmosphere encrease in an _arithmetical_ Progression; the Densities are said to encrease in a _geometrical_ Progression: which is a mathematical and pedantic Mode of Expression.

For _arithmetical_ Progression _here_ means no more than the Height of 1, 2, 3, 4, 5, 6, &c. &c. Yards, Fathoms, Roods, or any other equal Interval.

If then at the Height of one Yard, the Balloon has acquired (suppose) the Levity of 1 Pound; then, if this Levity encreases in geometrical Progression; (as twice 1 is 2,) it will, at the Height of 2 Yards, have encreased to 2 Pounds: and, as twice 2 is 4;) it will, at the Height of 3 Yards, have encreased to 4 Pounds: and, as (as twice 4 is 8;) it will, at the Height of 4 Yards, have encreased to 8 Pounds: and, (as twice 8 is 16;) it will, at the Height of 5 Yards, have encreased to 16: and, (as twice 16 is 32;) the Levity will, at the Height of 6 Yards, have encreased to 32 Pounds; and so on, _doubling_ the preceding Number; at the Height of each Yard, Fathom, Rood, Mile, &c. &c.

[101] _Whiston’s_ Tacquet’s Euclid, Book XI. Definition of a _right_ Cylinder, Art. 3, Page 166.

[102] Archimedes’s Theorems. Proposition 33, 34; at the End of _Whiston’s_ Euclid, Page 42.

[103] Inferred in the Chester Chronicle, Sept. 30, 1785.

[104] The Writer not having yet been able to procure it from the London Booksellers.

[105] See Chambers’s Dictionary under the Article +resistence+.

[106] See his “Navires des Anciens.”

[107] See “Gordon’s Principles of Naval Architecture.”

Also the Balzaes and Guaraes, in Ullòa’s Voyage to America, Book 4,