the great analqgyythpre is between the rifiny and falling
o f the water upon the flux and reflux of the fea, and this
of accumulating and.-extenuating the air, is a great afh
§nnVenflor.the truth o f fhe-hypothcfis. For as the- fea, -
over again« {hefc-^Sffildf.Ejj'exl rifes -artelfWells , by the
jmeeting o f the-tWo contrary tides p f flood,'; WK^pf- tlie
one comes from the S .W . along the ch.anjrtelvdfTEng'Idnd,
lan&th'eibtheriMpml:' the north-'; andi-pii1 the contrary,'
flutes (jtloWi-tjte ley cl upon the retreat'of the waters both
ways, in tlieetidem'fWbb-.; fo it is verygprpbabhvthat the
air may [gfp ’ and(flpw after the .u ' 17^ 5 hut by
reafon o f tire diverfityqf caufes the aicmayb.e
fet ;m; movi*g, slie times’ o f tliefe' ftuxes'and refluxes-,
.thereof ary purely cafual, and not reducible to any ru le ,.
as are the motion p f the ( , depen ing wholly ipqa
the regular epur-fe o f the moon. T hu s far , D r.
H alley. * - ,
. 28'S: The-following rules are given for jndgirrg o f the
weather by Mr ,. P a t r ic k , and. are edeemed the beft_
which we Have.
■ ' 1. T he riling o f the mercury p r e fa g e l’n genefal, farm
weather.;eaiul its falling,.foul Weather.; as rain,.mow,,
1 ng hi w 1 n ds ,a n di. fto r 111.
no; great diltaiice.off; for.the .northern
JBcnmarh',' Sweden,-, Norway,, aiid all that |ra'ft .rirortv..;.
wlicncc'north-eaflcrn Winds come, are fubje&rto -almoft
I continual froTt all the v r i n t e c l o w e r . a i t
, is Very mdeft emjoiSfed, and in that (hue is, brought
IdrheiuVnrd.sby. thpde/whrdsiiand being accurauhated b y
theftoppofitibift'OT the wefterly wind, blowing in the..
Ocean, the merdHTy müli'^èèas.bè p reuedto a morcthan
odd many height and'tat a (rnneurnng ciulTe,’the ftirink-
iiig- o f tbe lower partis.ó f the ai rfinto leller f oom b y cold,
■ inuft .neecls caulc a defeent o f tlHn-ncrnciapaj es o f tlit; at--
mpfphererto reduce the cavity made by lliit/contraption ,
tie an eqtidibnum^ffw
6thly, AffPr great, {forms ofw'ilirl. when the mercury
has been Very low,- it generally'riles again very fall. I
Once oblervcd it to nffc t..1 inch in It fs than 6 hours,
after a long continuenfafonn o f-'fou 1117 w e 1 fw i n d. 11.’he
r.eafon isj becaufe the air being very -mncK/rarefied, b y
the great evacuations which fuch’rcpntiimed (forms make
thereof, the neighbouring air-runs • inf mpte fwiftly to.
bring it Fo«an equilibrium; as We fee water, runs the
fader for having-a great, declivity.
- 7thly, T he variations are greater in the more northerly,
places as at Stockholm greater than at Paris (com-.
pared b y Mr. Paschall), becaufe the more northerly
places, have nfually greater flo rin s 'o f wind than the
more foutherly, wherèby.the mercury fliould fink lower
in that extreme; and then the northerly, winds bringing
the condenfèd andporidèrqiïs air fronytlienVigilbonrhood
o f the pole,, and that-again, being checked b y ’a fiiuther-
‘ ly wind at no great-diftance, and fönhéaped^müffof.ne-
cdfity make the mercury in fu ch cafe ftand higher in
.the other extreme.
Sthly, La ftly, this remark, that there.is little or no
variation near thé equinoöial, as at Barhadoes and St.
Helena, does above, all things confirm the hy.pothefis o f
■ the variable winds being the’ caufe/of theft: variations o f
the height Of the mercury ; fori in the places abover
named, tliere is always an -eafy, gale o f wind blowing
nearly upon the fame point,, viz E . N. E . ar Barhadoes,,
and E . S. E , at St. Helena, fo that there being no contrary
currents of.’’the air to exhand or accumulate it,.
> the atmofphere continues, much in the fame.date; .however,.
upon hurricanes (the-, raoft- violent.of dorms) the,
2 Iii very hot weather, the falling o f the mercury in-«
dicates thunder. :
_ 3. In winter, the rifing* indicates"froft'r andiiri ftoflyc
weather, i f th e mercury fall 3 or 4 'divifions, ffl /re V ill
follow a thaw. - But ’in a continued fro ft, i f the mercury
mercury handbeen dblerved - \ but. this is but Once
in two or-- three years',.and.ft foon,recovers its .fettled
date o f aboutfig( inches.,
1- 287. The- principal.objeiftioii/rtgainft this doélrine isj,
that 1. (n'ppoi:e/t!ie air fometimès -t-p move from, thole
parts where it is a] ready- evacuated below the equilibri-
um,and fometimes again' towards thofe-parts where itis
coiidesfcd'and.crowded abovesthe'mean date,:wliicb may
be thought contrary to the laws o f ' Statics, ami the
rules, o f the equibbrinmof fluids. | Bu t thofe who dial!
- conftder.'how When once an impetus is given' to a fluid
• bofiy, it is capable o f mounting above, its level, and1
checking! Others that have a.contrary tendency.-to de--
- feend by: their own gravity, will no longer regard this,
as a material obdacle;. but will, rather conclude, that. -
rife,./it wiU-'fnow. ' f
4. When foul weather happens foon after the falling
o f .the mere urv, expedf b i t libtl'e o f i t ; aiid o the;
contrary, e xp e it but little .fair Weather, when it proves
: fair Ihortly after the mercury has. rifen. ■ '
5. In foul weather when the mercury.rife's much'and.
high, and. fo tpritmues'for 2 or 3 days' before .the foul-
weather is quite'qlyeri then expeft a' coni iuuancc p f fair '
Weather to,follo w.
6. Tn fair weather when/the mercury falls much and’
low,.and thus-continues for. 2..01- 3 day before the.rain
comes, then expect-a great deal o f wet, and probably,
. high; winds, f
7. T he unfe'ttled' morion :of th e mercuiyi’deriptes uncertain
and changeable weather.
8. Yp.u are not fo dridtly tp o'bferve the words on the
plate', thougEm^/genpralthe weather agrees with tbern i
- For . if tbe merpuiy ..TJ-'. -’y t'. and.then rife to--
changeable,£t denotes fair weather, though not lo continue
fo'long as i f the mercury had rife.npjgher". V A n d.’
on the contrary, i f the mercury ftand at fa ir ‘and fall to '
. changeable, it denotes foul weather,, though not fo much
as if it had funk .lower.
289. T h e following rules are. ufefuf’td judge'/when-
the mercury if riflng or falling,;
1. I f ^He; fur face, of/the
flhg. '
2. If the.furface of. the mercury’ be. cqncsve,, it is
falling. _ , \'t .\
13. . I f the middle o f tbe mercury be plain, itis - neither!
1 rifing nor falling.; for mercury put into a glafs tube, will
detached thermometers expofed’ freely for a few minutes
to the'-ppen air in the (hade, .at the, two ftations ; thea-
t f o ; altitude pfd.the upper ftation above "the- lo.wer, in
:-Eiigli-flr fathoms, is1 thus expreffed 1
(i/b.g.: A ’— log. h Voj.454D ) x ( i f in-— 3z°>do,90?44.);
naturally have the parts ’adjacent to the tube cpri-
V^ ’ the mercuiy will adhere à I trie to the tube,
before you note its* height it. is proper-to {haké-thé baro- -
metpr-a- little, by giving it a little tap with the- kuuekle.^
■ On ■ i.'- ’
f 290. A Thermometer is an inftr-ument' to iricafure d if-,
ferCnt. degrees-of heat. I t tujgrj|j&r- à
bulb at the bottom, having the .biujb-and part of-the tube
filled with mercury; The . .tube...is
d o led 'a t thé -top-, -and the part d / . 1 by .the
. fluid is a vacuum. Againfbthe tube- there is aefcale/to
meafu-re the expanfion o f the fluid,under different tern"1
pe; for fluids expand by heat, and •cp.ntradt -by ,
sold. ■ A n inc'rfeafê o’f temperature will; therefore, .make
the flu d iifé iV ïV t liibc, and aulecreafe uf ’ ‘ i
will-make it fell.
291. T he thermometer 'now in-' life is that which'is "
conllnft.led b y Fahres-heit. ' P.n'ihishfcale, the fluid,
hand:, ar. 3,2 when it iuil begins to freeze,--and at 2.12-..1
when I ut into boil-i ig Vw iter ; at .temperate it (lands, a t ,
53 ; at fummer heat, at 76 ; at bloo'd heat, at. gfl.t I f
thé fealé be continued to Sob; it gives the heat o f hoilv
ing nicrcun ; and if it be continued d 11 \ id to .3.91
below o, it gives a degree of coldftWh'ich will- freeze ;
292. B y means' of. the barometer and th rmometer,
the altiuitlii/of a- inountain may be h)u 1 uh;to. ;;t:gTea 1. degree.
of ,{arclirac.y. T 1W following is the rule given--by
D r. Maskei,ynit in.his intruduhlion tp T aylor’ s L o garithms
; being thé. mean. between thofe^giyeffiby (General
R oy andrSir G eorge S kuc k eur gh . f ’
293» Given j’the altitudeshpf. the barometer at two
dations, with the heights -of, l-hhrcnheitV thermometer
attached, to thé barometer, and the heights o f two de-
' taih J.therhionieti s o f thi fame .kind,.éxpofed ..-to 'the*
air But died! cued frdih the fun at-tlie two ftations, to find
t-lih ; pcrpendit'hllar- altitude o f ode- ftatibn a hove the
pjheri W . . . ’ ..
■ ■ R u l e .. Put H for the ohfcrvcchheight1 o f the harome-
t or ait:tlut lohver ll.aLion, and h for that at the upper il a-
tton^D'fer’ the difference'- o f heights o f ‘Fahrenheit’ s
thermometer attached to thé barometer at the two fta:;
t-ions, .and oe-for th e mead o f the two heights oft the two
Where the upper lign :— is to -be fifed,- when the ther- -
’’mometei , attached /tp/the-i barometer is high eft’ at 'th e '
lower’ ftati'dni' (which-is• mod;' uflfalj; and;,the' lower'fign*
4-, whea i t it-lowed at the tower Hatton-
But/tb -render the rule more generally ufeful, we (hall -
put it- down in common; language. :
t- R u l e . T ake the difference oi.the coinrrion logarith'iis .-
(of. the-pbferved.heigilts ..of the barometers at tbe two
ftations, confidering -the firft four figures,g.excluflve o f
the index, as -whole numbers,, and^the remaining figures-
to the right as decimals, and [ubtra-R or add 0,454 multiplied
b y (lie difference, o f aititudes o f F ahrenheit’ s -
'thermometer attached to • the- barometer at- the two ftations,,
according as it was higheft at the lower or upper :
{ftatibn,-; and this is -nearly the required height. Then '-
mu’.tipi.y the height thus neadyifoundV,by the differenec-
. between ,the/mean of tbe two altitudes, o f' !the two -di-..
tached thermometers expofed to tbe air at, tbe two lla-
" tion ,tand320,.arid again that produdl by 0,02244, an d'
the laft'prbducl will be the correction o f the" altitude before
nearly, fou-nd’;; which added- to or fubtrhBed from th e -
feme,-’accofdih'g/as, the mean of tlie .t;wo altitudestpf then
.detached thermometers expofed 'to the air) was higher or
lower .than 32°, will, give' height-,pf/the upper
ftation above the lotver, in Englifli fathoms ;.' and this
mnltipl-ied' by 6, gives the tiiuh/altitudc in Englifli feet.
E x . Let-the ftate o f the1 „ ‘ aiid thermome-.
•tershfip; as- follows g to', find.-the . altitude-of one dtatiou-
aboyel.'&e othier..'’ I
Barometers. g j :Vë..;;Tfiéjdiómét'ers.‘ ■ -
. ' ■ iîovver 3O5-Ï#
Vitper 2 ,i.:y '
■ - -attached. “
47.
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1 - 1 ® M ■
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1
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