R I V 
But in proportion as a river, that has none 
of these obstacles in its bed, approaches to- 
wards its mouth, we see the velocity of its 
current augment, at the same time that the 
declivity of the bed diminishes. It is for this 
reason that inundations are more frequent 
and considerable, and do more damage in the 
interior parts' of a country, than towards the 
mouths of most rivers. 
In the Po, for example, the height of the 
banks made to keep in the waters, diminishes 
as the river approaches to the sea. At Fer- 
rara, they are twenty feet high: whereas, 
nearer the sea, they do not exceed ten or 
twelve feet, although the channel of the river 
is not larger in the one place than in the 
other. 
The mouths of rivers, by which they dis- 
charge their waters into the sea, are liable to 
great variations, which produce many changes 
in them. 
1st. The velocity and direction of the cur- 
rent at these mouths are in a continual varia- 
tion, caused by the tides, which alternately 
retard and accelerate the stream. 
2d!y. During the flowing of the tide, tire 
current of the river is lirst stopped, then 
turned into a direction entirely contrary 
throughout a considerable extent : if we may 
believe M. de Buffon, there are rivers in 
which the effect of the tides is sensible at 150 
or 200 leagues from the sea. 
3dlv. This state of things is a cause of a 
a great quantity of sand, mud, &c. being pre- 
cipitated and accumulated in the channel 
near the mouth. This continually raises and 
widens the bed, and at last changes it entirely 
into a. new place, or at least opens new 
mouths to discharge the waters at. The 
Rhine, the Danube, the Wolga, the Indus, 
the Ganges, the Nile, the Mississippi, and 
many other rivers, are instances of this. 
4thly. All these effects are less sensible at 
the mouths of little rivers, as their currents 
oppose no sensible obstacle to the flowing of 
the tides ; so that the ebb carries oft again 
what the flow had brought in. 
Whenever the course of a river through- 
out a considerable extent of country, ap- 
proaches towards a right line, its current 
will have a very great rapidity ; and the ve- 
locity wherewith it runs diminishing the ef- 
fect of its natural gravitation, the middle of 
the current will rise up, and the surface of 
the river will form a convex curve of suffi- 
cient elevation to be perceived by the eye ; 
the highest point of this curve is always di- 
rectly above the line of greatest current in 
the stream. 
Oil the contrary, when rivers approach 
near enough to their mouths for a sensible 
effect to be produced in them by the flowing 
of the tides; and also, when In other parts of 
their course they meet with obstacles at the 
sides of their channel ; in botii these cases 
the surface of the water at the sides of the 
current is higher than in the middle, even 
though tiie stream should be rapid. In this 
situation of things, the surface of the river 
forms a concave curve, the lowest point of 
which, or that of inflection, is directly over 
the line of greatest current. The reason of 
this is, that there are in this case two different 
and opposite currents in the river ; that by 
which the waters flow towards the sea, and 
preserve their motion even to a considerable 
R I V 
distance ; and that of the waters which re- 
mount, either by the flowing of the tide, or 
by their meeting with local obstacles, which 
form a counter current. 
An island in the middle of a river produces 
the same effect as obstacles at the sides, re- 
gard being had to the difference of situation 
of each. 
Eddies and whirlpools in rivers, in the 
centre of which there appears a conical or spiral 
cavity, and about which the water turns with 
great rapidity and sucks in whatever ap- 
proaches it, proceed in general from the mu- 
tual percussion of these two counter cu: rents; 
and the vacuity in the middle is produced 
by the action of the centrifugal force, by 
which the water endeavours to recede, in a 
direct ratio of its velocity, from the centre 
about which it moves. 
If rivers persevered always nearly in the 
same state, ihe best means of diminishing the 
velocity of the current when it is found too 
great for the purposes of navigation, would 
be by widening the channel; but as all rivers 
are subject to fr quent increase and diminu- 
tion, and consequently to very different de- 
grees of velocity and force in the current, 
this method is liable to produce very detri- 
mental effects ; for, when the waters are low, 
if the channel is very large in proportion, 
the stream will excavate a particular bed, 
j which, according to the irregularities of the 
1 bottom, will form various turnings and wind- 
j mgs with regard to the principal bed ; and, 
I when the waters come to increase, they will 
follow, to a certain degree, the directions 
which the bottom waters take in this particu- 
lar bed, and thereby will strike against the 
i sides of the channel, so as to destroy the 
banks and cause great damages. 
Ii would be possible to prevent in part 
I the bad effects proceeding from the current 
striking against the banks, by opening, at 
tho'e places where it strikes, little gulphs 
I into the land, dug in such a form and direc- 
j tiou as (hat the striking current should enter 
l and circulate therein, so as to destroy, or at 
least, greatly diminish its velocity. T his ef- 
fect would be felt for a considerable way 
down the river. 
This same method might probably be used 
with success against the destruction of bridges, 
weirs, &c. by the violence of the stream dur- 
ing floods. Such gulfs being dug into the 
outer side of those turnings in the river which 
are immediately above the place to be se- 
cured from the violence of the stream, would 
successively diminish its velocity, its force 
and dangerous effects, a considerable way 
down the river. 
RIV1NA, a genus of the monogynia order, 
in the tetrandria class of plants. The peri- 
anthus is four-leaved, coloured, and perma- 
nent, the leaflet oblong egged and obtuse ; 
there is no corolla, unless the caiyx is con- 
sidered as such. There are four or eight 
filaments, shorter than the calyx, approach- 
ing by pairs, permanent ; the antherx are 
small. The germ is large and roundish ; the 
style very short ; the stigma simple and Ob- 
tuse. The berry is globular, sitting on the 
green reflected calyx, one-celled with an in- 
curved point. There is one seed, jensform, 
and rugged. There are four species. It 
grows naturally in most of the islands of the 
West Indies. The juice of the berries of the 
R O R 097 
] plant will stain, paper and linen of a bright 
red colour, and many experiments Tirado with 
it to colour flowers have succeeded extreme- 
ly well in the following manner ; the juice 
of the berries was pressed out, and mixed 
with common water, putting it into a phial, 
shaking it well together for some time, till 
the water was thoroughly tinged ; then the 
flowers, which were white and just fully 
blown, were cut off, and their stalks placed 
into the phial ; and in one night the flowers 
have been finely variegated with red; the 
flowers on which the experiments were made, 
were the tuberose and the double white nar- 
cissus. 
RIX-DOLLAR, a silver-coin current in 
different parts of Europe. See Coin. 
ROACH. See Cyprinus. 
ROAD, in navigation, is a place of an- 
chorage at some distance from shore, where 
vessels usually moor, to wait for a wind or 
tide proper to carry them into harbour, or 
to set sail. When the bottom is firm, clear 
of rocks and sheltered from the wind, it is 
called a good road ; and when there is but 
little land on any side, it is termed an open 
road. The roads in his majesty’s dominions 
are free to all merchant vessels, belonging 
to his subjects and allies. Captains and 
masters of ships who are forced by storms, 
&c. to cut their cables, and leave their an- 
chors in the roads, are obliged to fix marks 
or buoys, on pain of forfeiting their anchors, 
& c. Masters of ships coming to moor in a 
road, must cast anchor at such a distance, as 
that the cables, & c. do not mix, on pain of 
answering the damages ; and when there 
are several vessels in the same road, the out- 
ermost to the sea-ward is obliged to keep a 
light in his lanthorn in the night-time, to ap- 
prise vessels coming in from sea. 
ROASTING. See Metallurgy. 
ROB, in pharmacy, the juices of fruit 
purified and inspissated till it is of the con- 
sistence of honey. 
ROBBERY, in law is a felonious taking 
away of another man’s goods from his per- 
son or presence again t his will, putting him 
in fear, *and of purpose to steal the same. 
West. Symbol. To make a robbery there 
must be a felonious intention ; and so it ought 
to be laid in the indictment. 1 H. II. 532. 
It is immaterial of what value the thing taken 
! is ; a penny, as well as a pound thus forcibly 
extorted, makes a robbery. 1 Ilaw. 34. 
If a man forces another to part with his 
property, for the sake of preserving his cha- 
racter from the imputation of having been 
guilty of an unnatural crime, it will amount 
to a robbery, even though the party was un- 
der no apprehension of personal danger. 
Leach’s Cro. Law, 257. 
If any thing is snatched suddenly from the 
head, hand, or pe son of any one, without 
any struggle on the part of the owner, or 
without any evidence of force, or violence 
being exerted by the thief, it does not amount 
to robbery. But if any tiling is broken or 
torn in consequence of the sudden seizure, it 
would be evidence of such force as woulep 
constitute a robbery: as where a part of a 
lady’s hair was torn away, by snatching a 
diamond pin from her head, and an ear was 
torn by pulling off an ear-ring ; each of these 
cases was determined to be a robbery. 
Leach’s Cro. Law, 264. 
By 7 G. II. c. 21, if any person shall, with 
