RAK 
tion at XQ, they will proceed to LM, in- 
tersecting each other at S, equally distant 
from X Q, as R is from T V : and as the 
rays, QT, XV, if they proceeded back- 
ward, would, after reflection, so fall on the 
surface, N O, as to be refracted into air pa- 
rallel to each other ; so X M, Q L, falling 
on the surface precisely in the same cir- 
cumstances, shall be refracted to the eye 
parallel to each other, and therefore will 
enter it copiously enough to cause a per- 
ception of their colour, (and so of tlie rest). 
The red rays, when emerging parallel after 
two reflections, are by calculation found 
to make with the incident rays, and there- 
fore witli the axis of vision, an angle of 
60° 57'. The violet rays, 'when emerging 
parallel, are found to make with their inci- 
dent rays, and therefore with the axis of vi- 
sion, an angle of 54° 7' : the other emerg- 
ing rays meet the axis of vision in the inter- 
mediate angles. From hence it is easy to 
explain the generation of the exterior bow, 
(fig. 12) in the same manner as that of the 
interior. It is to be remarked, that the or- 
der of colours in the exterior bow is the re- 
verse of that in the interior, and the reason 
of this appears in the above explanation ; 
for A E, which marks the direction of 
the violet rays in the outer bow, contains 
with A X, the axis of vision, a greater angle 
than A D, which marks the direction of the 
red rays, contains with the same axis. The 
reverse is the case in the interior bow. It 
is evident, (for a reason similar to that 
given in the case of the interior bow) that 
an exterior bow cannot be seen when the 
elevation of the sun is above 54° 7'. 
Rainbow, lunar. The Moon sometimes 
also exhibits the phenomenon of an iris, 
by the refraction of her' rays in drops of 
rain in the night time. 
Rainbow, marine, the sea bow, is a 
phenomenon sometimes observed in a much 
agitated sea, when the wind, sweeping part 
of the tops of the waves, carries them aloft, 
so that the rays of the sun are refracted, 
&c. as in a common shower. 
RAISING pieces, or Reason pieces, in 
architecture, are pieces that lie under tlie 
beams, and over the posts or puncheons. 
RAISINS, grapes prepared by suffer- 
ing them to remain on the vine till they are 
perfectly ripe, and then drying them in the 
sun, or by' the heat of an oven. 
RAKE of a ship, is all that part of her 
hull which hangs over both ends of her 
keel. That which is before, is called the 
fore-rake, or rake-forward ; and that part 
RAM 
which is at the setting on of the stern- 
post, is called the rake-aft, or afterward. 
RAKING, the act of cannonading a 
ship on the stern or head, so as that the 
balls shall range the whole length of the 
decks, which is one of the most dangerous 
circumstances that can happen in a naval 
action ; this is frequently called raking fore 
and aft, and is similar to what is termed by 
engineers enfilading. 
RALLUS, the rail, in natural history, a 
genus of birds of the order Grallae. Gene- 
ric character: bill slender, slightly com- 
pressed, and incurvated; nostrils small; 
tongue rough at the end ; body much com- 
pressed ; tail very short. There are twenty- 
two species, of which we shall notice the 
following : 
R. aquaticns, or the water-rail; is fre- 
quently to be seen in this island, and is 
about four ounces and a half in weight. It 
resides in moist situations, abounding in 
sedges and reeds, where it finds cover and 
security. It is timid and solitary, flies with 
considerable aukwardness with its legs 
hanging down, and shows great reluctance, 
even when much pressed by the sportsman 
and his dogs, to take wing. It runs with 
wonderful rapidity, and seldom rises in the 
air till it has fatigued both itself and its pur- 
suers, by an exhausting progress on its 
feet. It swims with tolerable ease, and 
where there are any weeds upon the water, 
will run over them with great lightness. 
It is migratory, and winters in Africa. Its 
flesh is good. See Aves, Plate XIII. 
fig. 1. 
R. porzana, or the water crake or skitty. 
This also is fond of low and marshy grounds 
in which are covers of reeds and rushes, 
and in which it shelters itself in security. 
It is extremely timid and sequestered, and 
is rarely seen in this island, eluding obser- 
vation by its perpetual vigilance and lurk- 
ing habits. Its nest is formed with singu- 
lar care of matted rushes, and materials 
which will float on the water, on which it 
remains tied, by some filaments, to the 
stalks of reeds, by which it is prevented 
from being carried away by the tide or 
current. This bird is in great esteem for 
the table. 
RAM, in zoology, the male of the sheep 
kind. See Ovis. 
Ram, battering, in antiquity, a military 
engine used to batter and beat down the 
walls of places besieged. The battering 
ram was of two sorts, tlie one rude and 
plain, the other compound. The former 
