RAI 



RAL 



exterior bow is formed by two reflections 

 and two refractions at the surfaces of the 

 drops of falling' rain. If the red rays of 

 any pencil, C D, (tig. 14) of solar rays, 

 after refraction intersect each other at It, 

 so that when reflected at T V, they may 

 proceed parallel within the drop, after a 

 second reflection at X Q, they will pro- 

 ceed to L M, intersecting' each other at 

 S, equally distant from X Q, as R is from 

 T V : and as the rays, QT, X V, if they 

 proceeded backward, would, after reflec- 

 tion, so fall on the surface, N O, as to be 

 refracted into air parallel to each other ; 

 so X M, Q L, falling 1 on the surface pre- 

 cisely in the same circumstances, shall be 

 refracted to the eye parallel to each other, 

 and therefore will enter it copiously 

 enough to cause a perception of their 

 colour, (and so of the rest). The red 

 rays, when emerging parallel after two 

 reflections, are by calculation found to 

 make with the incident rays, and there- 

 fore with the axis of vision, an angle of 

 50 9 57'. The violet rays, when emerging 

 parallel, are found to make with their in- 

 cident rays, and therefore with the axis 

 of vision, an angle of 54 7' : the other 

 emerging rays meet the axis of vision in 

 the intermediate angles. From hence it 

 is easy to explain the generation of the 

 exterior bow, (fig. 12) in the same man- 

 ner as that of the interior. It is to be re- 

 marked, that the order of colours in the 

 exterior bow is the reverse 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 with 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 some- 

 times 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, sweep- 

 ing 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 



the beams, and over the posts or pun- 

 cheons. 



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 which is at the setting on of the 

 stern-post, is called the rake-aft, or after- 

 ward. 



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 dan- 

 gerous 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 Grallse. Ge- 

 neric character : bill slender, slightly 

 compressed, and incurvated ; nostrils 

 small ; tongue rough at the end ; body 

 much compressed ; tail very short. There 

 are twenty-two species, of which we shall 

 notice the following : 



R. aquaticus, or the water-rail, is fre- 

 quently to be seen in England, 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 awkwardness, with it ; 

 legs hanging down, and shows great re- 

 luctance, even when much pressed bv 

 the sportsman and his dogs, to take wing. 

 It runs with wonderful rapidity, and sel- 

 dom rises in the air till it has fatigued 

 both itself and its pursuers, by an ex 

 hausting 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 migra 

 tory, and winters in Africa. Its flesh is 

 good. Sec Aves, Plate XIII. fig. 1. 



R. porzana, or the water crake or 

 skitty. This also is fond of low and 

 mai'shy grounds, in which are covers of 

 reeds and rushes, and in which it shelter? 

 itself in security. It is extremely timid 

 and sequestered, eluding observation bv 

 its perpetual vigilance an'd lurking habits, 

 Its nest is formed with singular 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 be- 

 ing carried away by the tide or currenf , 



