66 R H U 
this shrub is from three to four feet in height, branched 
towards the summit. Leaves alternate, ovate, acute, smooth, 
entire, nearly sessile. Stipulas twin, small, deciduous. 
Flowers corymbose, axillary and terminal, of a yellowish 
green colour, each standing on a long, slender stalk, which 
is furnished with a scale at its base. 
RHOPOGRAPHI, [’Pomy^aipoi, Gr.] an appellation given 
to certain painters, who confined themselves to low subjects, 
such as animals, plants, landscapes, &c. 
The same appellation has been also given to such as cut 
figures of men, &c. in box, yew, &c. in gardens. 
RHOSOS, a town situated on the gulf of Issus, at the 
eastern extremity of the Mediterranean sea, between two 
defiles, one of which led to Syria, and was called the 
“ Gates of Syria;” and the other formed by mount Amanus 
and the sea-coast, communicating with Cilicia, and called 
the “ Amanic gates.” Ptolemy places this town in Syria, 
and Strabo places it in Cilicia. After the death of Seleucus 
Nicator, Demetrius caused the statue of Fortune to be con¬ 
veyed hither. It was famous for the manufacture of earthen 
vessels, mentioned by Cicero, when he was governor of 
Cilicia, in a letter to Atticus. Sapor, king of Persia, burnt 
this city, after he had taken prisoner the emperor Valerian, 
A. D. 260. It was pillaged under the reign of Arcadius, in 
the year 404, by the Isaurians, a savage people, who inha¬ 
bited the mountains. Jupiter was worshipped in this town; 
and the statue of this deity was engraven on the medals of 
Rhosos. 
RHOX, a word used by some authors to express the 
tunica uvea of the eye. 
RHUABEN, a village of Wales, in Denbighshire; 6 miles 
from Wrexham. 
RHU'BARB, s. [ rhabarbarum , Latin; which Morin 
derives from the Gr. pa, in its medicinal sense of root, and 
j3a.a€acoi;, strange, foreign.] A purgative root. See Rheum. 
What rhubarb, senna, or what purgative drug 
Would scour these English hence ? Shakspeare. 
RHUBRA, a town situated on the southern coast of the 
island of Corsica, between the port of Syracuse and the 
promontory Graniacum. Ptolemy. 
RHUBRICATA, a town ofHispania, in the Tarragonese, 
in the country of the Lacetanians. Ptolemy. 
RHUBUNA, a town of Africa, on the northern bank of 
of the river Gira, between Artagira and Lynxama. Pto¬ 
lemy. 
RHUDA, a town of Asia, in Parthia, between Passa- 
carta and Simpsimida. Ptolemy. 
RHUDDLAN, a village of Wales, in Flintshire, anciently 
a place of considerable importance, being one of the most 
considerable towns in North Wales, and the residence of 
several of the Welsh princes. It still retains its elective 
franchise as a contributary borough. It is situated in the 
vale of Clwyd. Its castle, of which some detached towers 
still remain, was once a place of great strength, and of very 
great importance. It was built anterior to the Normam 
conquest. In 1646, having fallen into the hands of the 
royalists, it was dismantled by order of parliament. Its fonn 
was nearly square, and the walls were flanked by six round 
towers, three of which remain tolerably entire. The ditch is 
wide and deep, and on both sides faced with stone. In this 
castle Eleanor, consort of king Edward, was safely delivered 
of a daughter. Rhuddlan was made a free borough by 
Edward I., and endowed with numerous privileges and 
immunities; 3 miles from Disert. Population 831. 
RHUDEN. See Rutken. 
RHUDEN, Gross, a village of Germany, in Hanover, 
principality of Hildesheim, with 1000 inhabitants, and 
large salt-works. 
RHUMB, Rumb, or Bum, in Navigation, a vertical cir¬ 
cle of any given place; or the intersection of a part of such 
a circle with the horizon. 
Rhumbs, therefore, coincide with points of the world, 
or of the horizon. And hence the mariners distinguish the 
rhumbs by the same names as the points and winds. But 
R H U 
we may observe, that the rhumbs are denominated from the 
points of the compass in a different manner from the winds ; 
thus, at sea, the north-east wind is that which blows from 
the north-east point of the horizon towards the ship in which 
we are ; but we are said to sail upon the north-east rhumb, 
when we go towards the north-east. 
They usually reckon 32 rhumbs, which are represented 
by the 32 lines in the rose, or card, of the compass. 
Aubin defines a rhumb to be a line on the terrestrial globe, 
sea-compass, or sea chart, representing one of the 32 winds 
which serve to conduct a vessel. So that the rumb a vessel 
pursues is conceived as its route, or course. 
Rhumbs are divided and subdivided like points. Thus, 
the whole rhumb answers to the cardinal point. The half 
rhumb to a collateral point, or makes an angle of 45° with 
the former. The quarter rhumb makes an angle of 22° 30' 
with it. And the half quarter rhumb makes an angle of 
11° 15'. 
Sometimes navigators divide the 32 points into four quar¬ 
ters, and call the rumb next the east the first rhumb, the 
next to that the second rumb, &c. 
RHUMB-LINE, Loxodromia, is a line prolonged from 
any point of the compass in a nautical chart, except the 
four cardinal points; or it is the line which a ship, keeping 
in the same collateral point or rhumb, described throughout 
its whole course. 
The great property of the rumb-line, or loxodromia, 
and that from which some authors define it, is, that it cuts 
all the meridians under the same angle. 
This angle is called the angle of the rhumb, or the loxo- 
dromic angle. 
The angle which the rhumb-line makes with any parallel 
to the equator, is called the complement of the rhumb. 
An idea of the origin and properties of the rhumb-line, 
the great foundation of navigation, may be conceived thus : 
a vessel beginning its course, the wind with which it is driven 
makes a certain angle with the meridian of the place; and 
as it is supposed, the vessel runs exactly in the direction of 
the wind, it makes the same angle with the meridian which 
the wind makes. 
Supposing then the wind to continue the same, as each 
point or instant of the progress may be esteemed the be¬ 
ginning, the vessel always makes the same angle with the 
meridian of the place where it is each moment, or in each 
point of its course, which the wind makes. 
Now a wind, e. gr. that is north-east, and which, of con¬ 
sequence, makes an angle of 45° with the meridian, is 
equally north-east, wherever it blows, and makes the same 
angle of 45° with all the meridians it meets. A vessel, there¬ 
fore, driven by the same wind, always makes the same an¬ 
gle with all the meridians it meets with on the surface of the 
earth. 
If the vessel sail north and south, it makes an angle infi¬ 
nitely acute with the meridian, i. e. it is parallel to it; or 
rather sails in it. If it run east and west, it cuts all the 
meridians at right angles. 
In the first case, it describes a great circle; in the second, 
either a great circle, viz. the equator, or parallel to it. It 
its course be between the two, it does not then describe a 
circle; since a circle, drawn in such a manner, would cut 
all the meridians at unequal angles, which the vessel can¬ 
not do. 
It describes, therefore, another curve, the essential pro¬ 
perty of which is, that it cuts all the meridians under the 
same angle. This curve is what we call the loxodromic 
curve, rhumb-line, or loxodromy. 
It is a kind of spiral, which, like the logarithmic spiral, 
makes an infinity of circumvolutions without ever arriving 
at a certain point, to which it yet still tends, and towards 
which it approaches at every step. 
This asymptotic point of the rhumb line is the pole: at 
which, rvere it possible for it to arrive, it would find all 
the meridians conjoined, and be lost in them. 
The course of a vessel then, except in the two first cases, 
is always a rhumb-line; which line is the hypothenuse of 
a right- 
