SAI 



SAL 



rules of computation are founded on the 

 hypothesis that the earth is a sphere. 



3. Parallel sailing. The term denotes 

 the course of a ship sailing in a direction 

 either due east or due west, so as to sail 

 on the circumference of a parallel of lati- 

 tude. The determination of the ship's 

 place is obtained by knowing that, on 

 the globe, the length of a degree of a 

 meridian bears the same proportion to 

 the length of a degree of a parallel, as 

 the radius to the cosine of the latitude 

 in which that parallel is situated. 



4. Mercator's sailing. In this mode of 

 sailing, the earth's surface is supposed 

 to be projected on a plane, as on a Mer- 

 cator's chart (See Projection), in which 

 the meridians and parallels of latitude 

 are respectively parallel to themselves. 

 The ship's place is then determined by 

 the fact that the lengths of infinitely 

 small portions of the circumference of the 

 equator have to the lengths of corre- 

 sponding portions of a meridian, in any 

 latitude, the ratio that the radius bears 

 to the secant of that latitude. 



5. Great-circle sailing. This consists 

 in determining a series of points in an 

 arc of a great circle between two points 

 on the surface of the earth, for the pur- 

 pose of directing a ship's course as nearly 

 as possible on such arc ; that is, on the 

 curve of shortest distance between the 

 place from which she sets out and that 

 at which she is to arrive. 



6. Traverse sailing. This is a general 

 term for the determination of a single 

 course equivalent to a series of succes- 

 sive courses, whatever be the manner of 

 finding the lengths of the lines forming 

 the triangles. 



7. Oblique sailing. This consists in de- 

 termining the position of a ship by ob- 

 serving with a compass the bearings of 

 two or more objects on the shore, whose 

 places are given on a chart, and drawing 

 lines from those places so as to make 

 angles with their meridians equal to the 

 observed bearings : the intersection of 

 the lines gives on the chart the position 

 of the ship. This is sometimes called the 

 method of cross bearings. 



8. The term oblique sailing is also 

 applied to any problem in which (when 

 the triangles are not right-angled) the 

 distance of the ship from any object on 

 the shore, or of such objects from one 

 another, is computed by the rules of 

 plane trigonometry from bearings ob- 

 served at the ship when the latter is at 

 two or at a greater number of stations. 



9. Current sailing. This is the method 

 of determining the true motion of a ship 

 when, besides being acted upon by the 

 wind, she is moving in a current. 



10. Windward sailing. A term applied 

 to that mode of navigating a ship in 

 which the latter endeavours to gain a 

 port situated in the direction whence 

 the wind is blowing. The ship in this 

 case is made, by frequent tacking, to 

 sail as near as possible to the wind. — 

 Pen. Cycl. 



SAL AMMONIAC. Salmiac. Mu- 

 riate of ammonia. The native salt is of 

 two kinds, the volcanic, and the con- 

 choidal ; the former consisting of sal am- 

 moniac and muriate of soda, and found 

 in volcanic districts ; the latter consist- 

 ing of sal ammoniac and sulphate of 

 ammonia, found, it is said, in beds of 

 clay slate. Secret sal ammoniac is sul- 

 phate of ammonia, and was so named by 

 its discoverer Glauber. 



SAL PRUNELLA. Nitrate of potash, 

 fused and cast into cakes or balls. 



SALAMA'NDRIDiE. A family of 

 Batrachians, comprising the salamander, 

 the newts, and other species of lonp^ 

 tailed caducibranchiate reptiles, or those 

 which lose their gills before they arrive 

 at maturity, but retain their tails. 



SALICAOEiE {salix, the willow). The 

 Willow tribe of Dicotyledonous plants. 

 Trees or shrubs with leaves alternate; 

 flowers achlamydeous, amentaceous ; ova- 

 rium superior, 1 or 2-celled ; fruit coria- 

 ceous; seeds indefinite, comose. 



SALICARIiE. The Loosestrife tribe 

 of Dicotyledonous plants. Herbs with 

 leaves opposite, entire; flowers polype- 

 talous; calyx tubular; stamens peri- 

 gynous; carpella concrete; and a su- 

 perior ovarium with several cells. 



SA'LICYL. The hypothetical radical 

 of salicylous and salicylic acids, and 

 some other compounds. It was viewed 

 by Dumas as a higher degree of oxida- 

 tion of benzoyl. 



SALIENT ANGLES {salio, to jump 

 or bound forward). The prominent angles 

 in a zigzag line, which alternate with 

 the reversed or re-entering angles. The 

 term is frequently used in fortification, 

 but seldom in geometry. 



SALFFEROUS SYSTEM {sal, salt, 

 fero, to bear). A geological term applied 

 to the series of calcareous, argillaceous, 

 and sandy strata, which produce rock 

 salt or brine springs, and gypsum. The 

 series is also termed New Red Sand- 

 stone, from the prevalence of the red 

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