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Chambers, Ephraim, 1680 (ca.)-1740 / Cyclopædia, or, An universal dictionary of arts and sciences : containing the definitions of the terms, and accounts of the things signify'd thereby, in the several arts, both liberal and mechanical, and the several sciences, human and divine : the figures, kinds, properties, productions, preparations, and uses, of things natural and artificial : the rise, progress, and state of things ecclesiastical, civil, military, and commercial : with the several systems, sects, opinions, &c : among philosophers, divines, mathematicians, physicians, antiquaries, criticks, &c : the whole intended as a course of antient and modern learning
(1728)

R - rectification,   pp. 951-966 PDF (18.2 MB)


Page 954


RAI
Idea whereof will not be unacceptable.
Upon meafuring. then, the Rain faling yearly; its Depth. at a
Medium, is found as in the following Table.
t nAth Af P A TV falhRne VaarlV.  ad its Proportion in reveral Places-
Inches.
At Townley in Lanca/hire, obferv'd by Mr. TowXnle>,     2 .2
Upjminfter in Ejfex, by Mr. Derham,                 9 9
Zurich in Switzerland, by Dr. Scheutcher,         32 2
Pifa in Italy, by Dr. Mich. Ang. Ti/li,            43  w
Paris in France, by M. de la Hire,                 '9
Lifle in Flanders, by M. de Vauban.               24
Proportions of the RAIN of feVeral Years to one another.
At Upminfter.        At Paris.
1700     19 Inch. 03 Cent. 21 Inch. 38 Cent.
1701     I8      69       27       78
I 702    20      3 8      1 7     42
1703     23      99       I8       51
I704    IS5      81       21      20
1705     I 6     93       14      82
Proportion of the RAIN of the feLeral Seafons to one another.
Dphat
1 708   Inch.
Jan.   6 4i
FebrW  3 28
Mar.    2 65
Ap5qr.  125
May    3 3 3
June   4 9o
HafYa.28 8 o
[-lalf-Year.28    82                       i.Aafl-. tdJ.
Upminfl. Zurich.
inch.  Inch.
2 88   1 6
0 46     6
2  3 1 5
o 96   4 69
2 02   I 91
2 32 5 91
Io 67 17 31
1708
July
Aug.
Sept.
Oa.
Nov.
Dec.
f.,nrh at De-h a,
Pif ia. Uminfi
Inch.  Inch.
o 00 I II
2 27 2 94
7 21 I 46
5 33 0 23
o  13 0
o 0011 92
V.. nA 2 --
,IA  yIr I-'
icptha6
Zuricb
I nch.
3 V'
. 3 1'4
.3 0:
2 2.6
o 6_
''15 3~.
Przetcrnatural-RAINs, as of Blood, &c. are very frequent in
our Annals; and even Natural-Hiftories, yet; ifftridly pried in-
to, will be all found other things than Rain.
Bloody Rains, Dr. Meriet obferves, are, certainly, nothing
ele but the Excrements of Fafeds.
Accordingly, Gajfendus gives an Inftance of a bloody Rain in
France, which terrified the People; but which Peirijc found to be
only red Drops coming from a frt pf Butterfly that flew about
in great Numbers, as he concluded from feeing Cuch red Drops
come from them; from the Drops not being laid on Buildings,
or the outer Surfaces of Stones, &ec. but in Cavities and Holes;
and from thofe Walls only being tinged therewith that were next
the Fields, not thofe in the Streets; and the firnd only to a little
Height, fuch as Butterflies are ufed to fly to.
The fame Dr. Merret adds, that 'tis moft evident the Rains of
Wheat are nothing but Ivy-Berries, Swallowed by the Starlings,
and again cad forth by Stool.
An Inftance of fuch a Rain we have in the Philofoph. Tranf
from the Country about Briflol, by Mr. W Cole; who, upon
examining the Drops, found them to be the Seeds of Ivv-Berries,
blown down by fierce Winds from Towers, Churches, Chim-
neys, Walls, &c. where they had been left by Birds, chiefly
Starlings and Choughs.
The French have a Tradition of a Rain of Stones, in a Plain
fix or Ceven Leagues long between Arkes and .Marfeilles, call'd la
Crau, which is now quite cover'd therewith.
The Fable has it, that Hercules in his Engagement with Albion
and Bregion, in Favour of Neptune; wanting Darts, was afflided
by Jupiter with a Shower of thefe Stones, Ceen to this Day.
Another Account of their Origin, fee under the Article STONE.
RAINS, in the Sea Language, is all that Tradt of Sea to the
Northward of the Equator, -between 4 and io Degrees of La-
titude; and lying between the Meridian of Cape Verde, and that
of the Eaftermoft Iflands of the fame Name.
It takes its Name from the almod continual Calms, confdant
Rains, and Thunder and Lightning to a great Degree, found
there.  The Winds, when they do blow, are only fmall un-
certain Guds, and Shift about all round the Compafs; Co that
Ships are Cometitnes here detain'd a long while, and can make
but little way.
RAIN-BOW, IRIS, or fimply, the Bow, a Meteor in form
of a party-coloured Arch or Semicircle, exhibited in a rainy Skie,
oppotite to the Sun; by the refraffion of his Rays in the Drops
of falling Rain. See METEOR, RAIN, and REFRACTION.
There is alfo a fecondary or fainter Bow, ufually Ceen invering
the former, at Comne Diftance; and among Naturalifts we read
of Lunar Rainbows, AMarine Rainbows, &c.
The Rainbow, Sir Ifaac Newton obferves, never appears but
where it rains in the Sun-thine; and may be reprefented artifici-
ally, by contriving Water to fall in little Drops like Rain; thro'
which the Sun fhining, exhibits a Bow to a Speftator placed be-
tween the Sun and the Drops; efpecially if a dark Body, e. gr.
a black Cloath be dilpofed beyond the Drops.
Anton. de Dominis firfd accounted for the Rainbow, in 16II:
He explain'd at large how it was form'd; by refraation and re-
RAT
fleaion of the Sun-beams in fpherical Drops of Water; and con-
firm'd his Explications by Experiments made with Glafi Globes,
&c. full of Water. Wherein he was follow'd by Der Crtes, who
mended and improved on his Account: But as they were both
in the Dark as to the true Origin of Colours, their Explications
are Defeetive, and in Come things erroneous; which 'tis one of
the Glories of the Newtonian Doarine of Colours, to fupply and
corre&t.
Theory of the Formation of the RAIN-BOW.
To conceive the Origin of the Rainbow, let us confider what
will befal Rays of Light coming from a very remote Body, e.
gr. the Sun; and falling on a Globe of Water, fuch as we know
a Drop of Rain to be.
Suppofe then ADKN (Tab. Opticks, Fig. 45.) to be a Drop of
Rain, and the Lines EF, BA, ON, to be Rays of Light com-
ing from the Centre of the Sun; which, by reafon of the im-
menfe Diftance of the Sun, we conceive to be Parallel. See Pa-
rallel RAY.
Now the Ray BA being the only one that falls perpendicularly
on the Surface of the Water; and all the reff obliquely; 'tis eafily
inferr'd that all the other Rays will be refradted towards the Per-
pendicular. See REFRACTION.
Thus the Ray EF, and others accompanying it, won't go on
ifrait to G; but as they arrive at HI, defle1ta from F to K, where
Come of them, probably, efcaping into the Air, the reft are re-
fleited upon the Line KN, fo as to make the Angles of Inci-
dence and Reflexion equal. See REFLEXION.
Further, as the Ray KN, and thofe accompanying it, fall ob-
liquely upon the Surface of the Globule; they cannot pa1s out
into the Air, without being refraafed, fo as to recede from the
Perpendicular L M; and therefore will not proceed ftraight to Y,
but defleca to P.
It may be here obferv'd, that Come of the Rays arriving at P.
do not pafs out into the Air, but are again refleaLed to Q; where
being refracted like the relt, they do not proceed right to Z,
but declining from the Perpendicular TV, are carried to R: But
fince we here only regard the Rays as they may affeat the Eye
placed a little below the Drop, e. gr. at P, thofe which defle& from
N to Q, we fet afide as ufelefs, becaufe they never come at the
Eye. On the contrary, it is to be obferv'd, that there are other
Rays, as 2, 3, and the like, which being refle6ted from 3 to 4,
thence to 5, and from 5 to 6 may at length arrive at the Eye
placed beneath the Drop.
Thus much is obvious: But to determine precifely the Quan-
tities of Refradion of each Ray, there muft be a Calculation:
By fuch Calculation it appears that the Rays which fall on the
Quadrant AD, are continued in Lines, like thofe here drawn in
the D~rop AD KN; wherein there are three things very confi-
derable: Firj'1, That the two Refraffions of the Rays in their In-
grefs and Egrefs are both the fame Way, Co that the latter does
not defiroy the effecl- of the former. Secondlt~y, That of all the
Rays pafng out of AN; NP, and thofe adjoining to it, are the
only ones capable of affeding the Senfe; as being fufficiently
clofe or contiguous; and becaufe coming out parallel; whereas
the rea are divaricated, and difpersd too far to have any fenfible
Effe&, at lead to produce any thing Co vivid as the Colours of
the Bow. Thirdly, That the Ray NP has Shade or Darknefs un-
der it: For fince there is no Ray comes out of the Surface NA,
'tis the fame thing as it the Part were cover'd with an Opake Box
dy.  We might add, that the fame Ray NP has Darknefs above
it; Cince the Rays that are above it are ineffeitual ; and fignify
no more than if there were none at all.
Add to thefe, that all the effedtual Rays have the fame Point
of Refled)ion, i. e. the parallel and contiguous Rays; which a-
lone are effectual after Refraclion, will all meet in the fame
Point of the Circumference; and be refle6ted thence to the
Eye.
Further it appears by Calculation, that the Angle ONP, in-
cluded between the Ray NP, and the Line ON drawn from the
Centre of the Sun, which is the Angle whereby the Rainbow is
diftant from the oppofite Point of the Sun, and which makes the
Semidiameter of the Bow; contains 410 30'  The Method of
determining it fee hereafter.
But fince betide thofe Rays coming from the Centre of the
Sun to the Drop of Water, there are many more from the le-
veral Points of its Surface; there are a great many other effe-
6tual Rays to be con idered; epecially that from the uppermolt,
and that from the loweft Part of the Sun's Body.
Since then, the apparent Diameter of the Sun is about i6 Se-
conds, it follows that an effetual Ray from the upper Part of
the Sun will fall higher than the Ray EF, by i6 Seconds: This
does the Ray GH, (Fig. 46.) which being refrafted as much as
EF; defledts to I, thence to L; and at length emerging equally
refradted with the Ray NP, proceeds to M; and makes an An-
gle ONM, of 4I1 14' with the Line ON.
In like Manner the effeetual Ray QR coming from the lowefi
Part of the Sun, falls on the Point R, I6 Minutes lower than the
Point F, on which the Ray EF falls; and being refrafted declines
to S; whence it is refledfted to T; where emerging jinto thejAir,
it proceeds to V; Co, as the Line TV, and the Ray OT contain
an Angle of 4i and o6.                            A gat
7 IS 34
--nth _.. --.1.h - ,
-
11 --
t! I A V _
iHaltYt
tr-1d- I---l.
( 9-4 )


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