neveV puffes the walls o f the city; In Italy there is a
wiud called, the Italians, Sirocco'. ~ I t blows for l£ve-
ral days, and-its mean heat is about 1 120 o f Fahrenheit’ s
thermometer. I t is fatal to vegetation, and (leftru&ive
to the inhabitants; depi^fimg their fpirits, and fufpend-
ing the power§ 'o ffd ig e ftion fo that they who v^ithy;
t-o eat a heavy.>fupper; # M j thefe-winds preva ila|e fre-'
quently found dead thene xt morning. I t is felt with pe*
culia* violence atj Palermo, where the inhabitahfs' ftuit
their, doors .and windows; and where there are no fh utters,
they hang up wet blankets, and feivanls are employed
to keep.them wet. | No-hody ventures out,- i f he
can poffibfy avoid.it;
- 280. Mr. B ru c e , in relating the particulars o f his
jpurney arcroik.the defarts o f Africa, mentions prodigious
pillars o f faad, moving with great velocities. EleveO ofv
them appeared at once, at the diftance o f about three
miles from-him ; the_greateft diameter _of the large ft was,
eftimated at ten- feet. -The fame phenomenon appear
ed again within, a few. days after ; more pillars in number,
hut lefs ia fize. T h e y began immediately after fun
rife, and his rays Alining through them, gave them the
appearance o f pillars o f fire.
28 1 . There is a phenomenon called a water fpout,
hanging under-a deep cloud* in the form q f a cone with
the vertex downwards ; and under it the fea boils up,
and riles in a conical form; thefe two cones fometimes
meet, and they -generally begin to appear together; -but
fometimes the boiling o f the fea.appears firft. T he po-
fitfon o f the -eones-is-moftly perpendieularly to the fea,
but fometimes it is oblique; and! fometimes the fpout is
in the form o f a curve. T h e y "frequently difap.pear fud-
denly, and fometimes they move for a confiderable. fpace
before they break. T he form o f the water fpout is
more properly that o f a fpeaking trumpet, ihefqMler
end being downwards; Sometimes thefe water fpouts
appear at land. When they appear at fea, and are ap-.
proachinga fhi.p, it is faid that, the failors fire at them:
and break them ; as it might be dangerous, i f they were
to meet with a fliip and break over it. I t is with good
reafon fuppofed that this is an electrical phenomenon
for they generally appear in months which are fubjeCt to
thunder ftoims, and are commonly preceded, accompanied,
or followed by lightning, rain, or hail. Flafhes of1
light have been feen about them. But the moft" re-:
markable cijcumftance is, that they have been difperfed
b y prefenting to them fharp pointed kniye^or-fwords..
T h e analogy'alfo between a- water jfpout and ele&rieity
may be ftiown, b y banging a drop o f water on the under'
fide o f a plate o f brafs connected w ith the prime conductor,
and placing a- veflet o f water under, a t a fmall diftance
; then upon working the machine, the water will?
defeend from the_drop in a conical form, and the"'water
in the veffel will rife up under i t in the. form o f a con e ; 5
refembling 'v ery accurately the water fpout, and ■ the
afeent o f the water in' the fea under. I f we therefore
'fdppofe; the cloud to M ftrongly' charged with the elec--
trie matter, we have Caufe fufficient to fblve the phaeno- •
meuon. This theory o f water, fpouts is confirmed by
qne/.which M r, F o r s t e r " gives an account o f i|
his vbya^^rotui^: the^^orld.-f p)nv\thk teoaft 3 ofi, New
Zealand, he faw ■’the water ins' a fpace | o f yo orC 60
furlongs/niovetowards its centre,"and -thère rifing infc?
vapour, b y the - forcer o f the whirling motion which| it
had, afee-nded in a fpiral .form : toward|& the, clouds ;
direCtly over .which The cloud defeended in a gradually
tapered Tong'{lender tube, whi'ch foon united with the
afeending spiral in.a cylindrical form. T he water was
Whirled upwards wfth g reat yiofedc^ in anda'p--
• pearedttp leave! a hollow fpace in the middle; fo that ié
feemed fo harm aikfificfw'. tu b e f andfkqs \vas'l^h.deéed'
probable, as it looked exaCtl'y like1 a hollow glafs tube.
A f te r fome time, the f column' became - inciirvated^ :and
then broke; with |he appearance o f a flafh o f lightning.
2*82. A whirlwind is a wind which rifes fuddenly ; is
extremely rapid and impetuous, taking up' ;aljfight-Tub-1
fiance from* the earth which it may meet with,“ a ^ c a f t y -
ing^ them up in a fpiral motion;" - ©r . F R l i n fupi
poles that a whirlwind, and a Water fp0lit1pr0ceed‘ from'
the fame caufe ; and this opinion is ft rengthened by the
following circumftances. T h ê y have each JSl progrèffivq
and circular motion-; they^ufiiaMy«rife after calms, and
great heats; and' mqft freqüentdy-happen in warm, ‘latitudes
; the wind blows every-way both to the: whirlwind,
and water fp o u t; and a water.fpout, h^s moved-fiom the'
fea to the land and producèd ^1 the effects tóf a whirlwind.
T h e y are both o f them probably therefore the
effects o f the "deCtirical fluid.;" ;/
& k f h e B ^ qm ep e r , ?
283. -The Barometer is-an inftrument to meafiire -the
w e ight or .preffure o f the atipofphere, andf ipj^i well,
known, thatJ t is unneceflkry here to defcrihe.it. -Su^ce
;to fay, tnat -the air ia the 'glafs, tube is fuppqrtèd, by
the.preffure o f the air-upon the mercury in • t-he^bafp.H, i-n
which the lower and open end ofjthe tube isrimmerfed ; -
and the fpacê in the tube above 4he m&JÊQ%y is a vacuum,,
When therefore thé p reflurèVof the^air i|^iin,crèaft<d» the
mercury mu ft-rile ia the tube and when, the preffure Is
di min ifhed, the mqrcury mu ft fall. 'JJp^nTh,e level o f *
the^ far face o f the earth, the limits' qfjthe: -height o f the
mercury in the tube, above the fyifkce-of th3g ^ïeroufy inr
the-bafon, is from, 28- to 3 r inches; -a graduated fcale/
is therefore placed agairift theifubefrom 28 to 31 inches,
in order to afqertadn the height ;pf the merqury in-the
tube. Bu t thofe' barometers wlifch afe madq to mea-
fure the heiglifes o f pp.untain'8^ar>e graduated pinch low - ;
er ; becaufe, as you afeend in the atmofphere>. the mercury
falls. _ When the mercury ftands at tbe^ltitfude of-
30 inches, thé preffure of'tHe air*üpön every fquare inch
o f the earth’ s furface is about 15 lb. avoirpupoife. A t
any-other altittide.'<^the mercury, the-preffure will be
in proportion to the altitude. Hence, i f we take ‘.the%r-1
face o f a.middle-fized map to'be I4i-fquare feet, when the
air is lighted,' its preffure o,n him is 13, 2 tons, apd when
heavieft it is 1.4, 3 tons.; the difference o f which is 2464
lb. This difference o f preffures muff greatly affe'61 us
in refpe®> SK-riv
to ;* moee-^^SwI^wheh
fudden '1 he pi' f i l e o f (1 ,'Vf r'npoh tl e" " ’liHc fn itjc i
'Dr. Halley's Me uni Gtl ' /
:n « Barometer^ upon.
SSsjeWaB i|yersd:tiB>es,' it,; ec - ea itrperater'lo^
e,b rthe\ppncjpar
(n^roirt'eter.
Jfii c lfli Ss* tl 11, vlieii
W fflgoWWdttr lo w j ,
' z t U y j ; g o o d , feWfed'^weath'e^ the' mercury
is.jgei ei ajjy- mgh.', ,
• 3dly, TSipipii very great winds, tH', ugh tRj j Ia not ac- ■;
com ji^ffieil with J i < tlreimefcuiy' flhks'lp:nieit , 6 f all, i
with relation to the1 ,,poiut'of _the cpmpais the
Th'd gfeateft "EeiglitS o f
%^°d upon iCafterij' a i; if er]y
m-M: ■' ■i.-
■ «reather,
■ 6thly, A f te r vei-y great- fto ms o f u ihd, ,wht n (ht
fiu i& ffib r low, I r g c leE fflft j jto very
f f i V ^ ^ " * '
■’ -p tuly 1 alt&an’
'ihejiahomethr th^LtM^e'
HtSily, near them, thofe ,ac-
Gounts aye have had from other , and my owji obferya1
A K x f i . or no variatfen p f .Hie
freight o f .£he mcrOuryi 'in; all weathers.
H?H®TPcsSjd£i^e‘ that the principal caufe o f
the .rife-andirfflyoWfie, rnercury, is ’from"the variable
winds'; jvhid®!. are' found; In the temperate.zones, ahth
o fid uudfft iny .1 t>e in Knblanl is lrioit f,clo-
rfdiis'. ' .a
'J2.S6. A feconE " . uneertain'h-xhalafion and
precipitation o f the yapour^'lo'dgi'hg' 3n the air, wiiere'by
it come to be at one ti ne more c iov dtd^than', ioffiefj
ahd 'cpnfequeritly heavier ; but this.latter i n a . great ’
meafiife depends upon, thenfofmer. Now from thefe
principles X lh!all eifSeayonrifo1 explicate ;tlie feveinl phm-
J oft'h^hltplseter, taMng L:hetn'ih ui^^m^i-breler
I laid .themifbwn. _
' i l l , ^he..Tn'ei;C.irry b'eingTioyv'I'ralnef it tpt.rain, qes
cauifei'the air beih'gl^lit, theiy.ppp'iirs .are no longer fup-
ported thereby, bf:in^ become .ibYbi/icalfy hcavieiythan
the meuHimi-v^nefein th*y floated, j fo that they, defeend,,
toward8 the earth, meeting, . i:,
acjueous •particles', they'iV&rp'dhi'tS'th'gether “i j i,a
little,, drops :p f rain. j | n t i the iriercuiy’ s being at one"
time1 loiVer than rat. anotjier, is the effefl o f two "contrary,
winds blowiiigr/riiiH the place .'whererflii.e barome-
tef Bands, ^hfetehyitn'eair bMnalE place iSyGairied' both
ways from it, :ajn'd , , , j * ' iT, , , . C -s
, o f air is diminiflied, and accordingly the mercury Aiks-
As-for inliaflcc,. if’fpb.thc German Ocean it fliould blow a
gnle o f Weiterly wind, and at the fame time an caflerly
If in Prance it (hould blow a
1 wind, and in Scotland a foutherly, it mult be
granted me that, that part o f the atmofphere impendant
over iEny/aniif would thereby be exhaufted and attenuated,
and; the mercury ivouldifub.iide^aiiS the vapours which
■ bt^r^'(lpa:^a ip., thlm) parts o f Lbe ‘air ;p f equal gravity
' Vrifhf thP^^l^^T^Guld.iinfc to the earth.
2dly, The great height o f the barometer is occafioned
; 1>7 two contra y .winds blowing towards the place o fob -
fe r^ ^ J lk whyrelwj the air o f other places is brought
’ that tlie incumbent cyiin-
o'der o f nil beingincreafed both in height and weight, the
l? ?W ^ S p e ffe 3 tM^?Y-iu®jneeds rife and Hand high,
as. Iran'g^.as^1 . " . V blow ;. and1 ' i
nn be i n g ^ i t h e vapours are belter fuf-
p e i n c h n a t i p n to 1 i j
and fafl down in drops wtncE is. the reafon o f the fe-
rene good weather, which aWepds'ijilie greater heights o f
V the1 m e r e u r y j ;
\ :3.®y-)' The mere finks thefowett of all. by the very,
| l | | i l motion o f the air in ftoims'pfwind. Eor the traft,
earth’s furface,- vvlie^e'inLtliefe winds
rage, not. extending all round the .globe, that llagnant air
'^^wh;i^le|xh^^^|li^feewifel^iat.1,op,thefides1 cannot
come in fo fall; as to fupply the evacuatioii made b y ■
yhifwift a' current; fo that the air. muftih.epelfarilyibe at-
tejiiia'tfe'd when and where B e faid winds,continue to
blow,;.;and that more or lefs according tb their Wlence;
ad^ifMjtvhTc^thM'^^l’moi'isiontal'mPtibn or,vthe air
."*f -l|v^may in .alb, probability take off
■ j^ ^ ^ ^ pio^ ^ ^ ap^ idichlaf gteffure thereof: dnd the
g r fa t taafyr.of Ms|parti4es 'is the reafon why the vajiQuis'
are Tipipateakijd- do ' lypf pondeafe, into drops fb
^ t o form rdfijj bfchei^iie'fhfc. natural sepnfe^uence o f
• 4thly, The mercury Hands the higheft upon an eailer-
■ ly jr no th-i ill rjy ivind, becaufe in the. great iHinrv
Ode on, 'o i this lull th e :|||p degrte ofy^rth-j^f itiide, the,
wefierly and fouth7wefterly winbs -b|pw,.a|mj0ft always
ti® & w that ^®seVer here the -vyiria .epnjeSjup
a'nd north-eaft, it is fare to be.chpiSteS by ai contrary g^le,
’ ..whciiefoPe^according :
to what is madej put ?m j4ur®|asdu'ii*arfc, th'e air muft
jn&ds'ifii heaped.:.pver this liflanff, brtd cp.iifeqfiently tlie
>rn'erouiyirnuft ftand jughyVa^^ffin;/is thefe'g,yjnds'. blow. ('
®p,|-lipid! jKuij: in \ni/<^ijStc>
ruletforrothets...awheie' the vigiijj's are .uoefee different cir-
cumftances; and I have fometimes feen the mercury
here as low as 29 inches, tipon an eaftprly wihxl j huti
■ then-, it' hleiv exceeding luud, and 'fo comes to be ac-.
counted for by what wa bbferyed upon the third.
1 T ' f i t , Jt U
* '5thly,; In calm* frofty weather the mereury generally,
ftands^high, beeaufe (as. I conceive) it feldom freezes
but when th w fid co nes out o f they isorthenrandnorth -
eaftefif cyahrters, or at leaf! iinlefs thefe winds1 Hlow'at