HUE 



KUL 



RITBY. See CoiiuwnrM. 



R ii v, in heraldry, denotes the red co- 

 lour wherewith the arms of noblemen are 

 blazoned ; being 1 the same which, in the 

 arms of others, not noble, is called 

 gules. 



RUDTJECKIA, in botany, so named 

 from Olaus Rudbeck, father and son, pro- 

 fessors of botany at Upsal, a genus of the 

 Syngenesia Polygamia Frustranea class 

 and order. Natural order of Composite 

 Oppositifoliss:. Corymbifene, Jussieu. Es- 

 sential character : calyx with a double 

 row of scales ; crown of the seed a four- 

 toothed rim ; receptacle chaffy, conical. 

 There are seven species. 



RUDDER, in navigation, a piece of tim- 

 ber turning on hinges in the stern of the 

 ship, and which, opposing sometimes one 

 side to the water, and sometimes another, 

 turns or directs the vessel this way or 

 that. The rudder of a ship is a piece of 

 timber hung on the stern posts by four 

 or five iron-hooks, called pintles, serving 

 as it were for the bridle of a ship, to turn 

 her about at the pleasure of the steers- 

 man. The rudder being perpendicular, 

 and without-side the ship, another piece 

 of timber is fitted to it at right angles, 

 which comes into the ship, by which the 

 rudder is managed and directed. This 

 latter properly is called the helm or til- 

 ler; and sometimes, though improperly, 

 the rudder itself. The power of the rud- 

 der is reducible to that of the lever. As 

 to the angle the rudder should make 

 with the keel, it is shown, that in the 

 working of ships, in order to stay or bear 

 up the soonest possible, the tiller of the 

 rudder ought to make an angle of 55 

 with the keel. A narrow rudder is best 

 for a ship's sailing, provided she can feel 

 it; that is, be guided and turned by it : 

 for a broad rudder will hold much water 

 when the helm is put over to any side ; 

 but if a ship have a fat quarter, so that 

 the water cannot come quick and strong 

 to her rudder, she will require a broad 

 rudder. The aft-most part of the rudder 

 is called the rake of the rudder. 



RUDOLPHIXE Tables, a set of astro- 

 nomical tables that were published by the 

 celebrated Kepler, and so called from the 

 Emperor Rudolph, or Rudolphus. 



RUELLIA, in botany, so named in ho- 

 nour of Joannes Ruellius, a genus of the 

 Uidynamia Angiospermia class and order. 

 Natural order of Personatae. Acanthi, 

 Jussieu. Essential character : calyx five- 

 parted ; corolla subcampanulate ; stamens 

 approximating by pairs; capsule opening 

 by elastic teeth. There are forty-three 



species. Swartz observes, that the Ruel- 

 lise are ver\ nearly allied to the Justicize 

 in their natural order, fiower.s, fruit, and 

 habit. 



RUIZIA, in botany, so named -in ho- 

 nour of Don Hipolito Ruiz, a genus of the 

 Monadelphia Polyandria class and order. 

 Natural order of Columnifene. Malvaceae, 

 Jussieu. Essential character : calyx dou- 

 ble, exterior three-leaved ; styles ten ; 

 capsule ten, one-celled, two-seeded, close- 

 ly cohering. There are three species, 

 all natives of the Isle of Bourbon. 



RULE, in arithmetic, denotes an ope- 

 ration performed with figures, in order 

 to discover sums or numbers unknown. 

 The fundamental rules are addition, sub- 

 traction, multiplication, and division. But, 

 besides these, there are other rules, de- 

 nominated from their use ; as the rule of 

 ALLIGATION, FELLOWSHIP, INTEUEST,PIIAC- 

 TICK, REITUCTIOX, Sec. which see in the 

 alphabetical order. 



RULE of Three, GOLDEN Rule, or RULE 

 of Proportion, is one of the most essential 

 rules of arithmetic ; for the foundation of 

 which see the article PROPOHTION. It is 

 called the Rule of Three from having' 

 three numbers given to find a fourth ; 

 but, more properly, the Rule of Propor- 

 tion, because by it we find a fourth num- 

 ber proportional to three given numbers : 

 and because of the necessary and exten- 

 sive use of it, it is called the Golden 

 Rule. But to give a definition of it, with 

 regard to numbers of particular and de- 

 terminate things, it is the rule by which 

 we find a number of any kind of things, 

 as money, weight, &c. so proportional io 

 a given number of the same things, as 

 another number of the same or different 

 things is to a third number of the last 

 kind of thing. For the four numbers that 

 are proportional must either be all ap- 

 plied to one kind of things ; or two of 

 them must be of one kind, and the re- 

 maining two of another : because there 

 can be no proportion, and consequently 

 no comparison of quantities of different 

 species : as, for example, of three shil- 

 lings and four days; or of six men and 

 four yards. All questions that fall under 

 this rule may be distinguished into two 

 kinds: the first contains those wherein it 

 is simply and directly proposed to find a 

 fourth proportional to three given num- 

 bers, taken in a certain order: as if it 

 were proposed to find a sum of money so 

 proportioned to one hundred pounds, as 

 sixty-four pounds ten shillings is to eigh- 

 teen pounds six shillings and eight-pence, 

 or as forty pounds eight shillings is to six 



