SEC 



SEE 



waxy-looking fusible substance, found on 

 the Baikal lake in Siberia. 



SEAMS. Thin layers which separate 

 two strata of greater magnitude. 



SEASONS OF THE YEAR. The 

 four quarters of the year, commencing, — 

 the first, or Spring quarter, when the 

 sun enters Aries ; the second, or Sum- 

 mer, when he enters Cancer ; the third, 

 or Autumn, when he enters Libra; the 

 fourth, or Winter, when he enters Capri- 

 corn. The variety of the seasons de- 

 pends on the uniform direction of the 

 axis of the earth ; this is always carried 

 round parallel to itself, and pointing 

 always to the same vanishing point in 

 the sphere of the fixed stars. 



SEBA'CIC ACID {sebum, lard). An 

 acid obtained from the oleic, or from any 

 of the fats which contain this acid. Its 

 salts are called sebates. 



SECANT {seco, to cut). A line which 

 cuts another line. In trigonometry, it is 

 a straight line drawn from the centre of 

 a circle to one extremity of an arc, and 

 produced until it meets the tangent to 

 the other extremity. The secant of an 

 arc is a third proportional to the cosine 

 and the radius ; hence, if the radius be 

 taken as unity, the secant is the recipro- 

 cal of the cosine. See Trigonometry. 



SECOND. The sixtieth part of a 

 minute, in calculations either of time or 

 of angular measure. See Hour. 



SECOND (in Music). An interval 

 producing a discord, the rarfio of which 

 is 9 ; 8. There are three kinds of second, 

 the minor or semitone, as EF; the 

 major, or CD; and the extreme sharp 

 second, as CDJf. 



SECONDARIES. Secondary circles. 

 In Astronomy, all those circles on the 

 sphere which intersect a primary circle 

 at right angles, passing through the axis 

 and the poles, are called secondaries. 



SECONDARY STRATA. An exten- 

 sive series of the stratified rocks which 

 compose the crust of the globe, with cer- 

 tain characters in common, which distin- 

 guish them from another series below 

 them called primary, and from a third 

 series above them called tertiary. 



SECRETION {secernn, to separate). 

 A general term for that function in ani- 

 mal and vegetable physiology, by which 

 certain products are secreted or separated 

 from the circulating fluid, — from the 

 blood in animals, from the sap in plants. 

 The same term is also applied to the 

 products so secreted or separated. Thus, 

 the liver secrttes bile, and bile is called 

 299 



the secretion of the liver ; the tuber 

 secretes starch, and this is termed a 

 secretion of the tuber. 



SECTOR {seco, to cut). A sector of a 

 circle is the figure contained by two radii 

 and the arc between them ; it thus differs 

 from a segment, which is included by an 

 arc and its chord. A sector with a right 

 angle is a fourth part of a circle, and its 

 arc is called a *' quadrant." The term 

 sector is also applied to a mathematical 

 instrument, the purpose of which is to 

 facilitate the graphical determination 

 of proportional quantities; hence it is 

 termed by the French the compass of 

 proportion. 



SECTOR, ZENITH. A peculiar mo- 

 dification of the altitude and azimuth 

 instrument. It is adapted for the very 

 exact observation of stars in or near the 

 zenith, by giving a great length to the 

 vertical axis, and suppressing all the 

 circumference of the vertical circle, ex- 

 cept a few degrees of its lower part, by 

 which a great length of radius, and a 

 consequent proportional enlargement of 

 the divisions of its arc, are obtained. 



SECULAR and PERIODIC. In 

 Astronomy, any deviation from the mean 

 motion or mean orbit of a celestial body 

 is called an inequality, and the numeri- 

 cal expression of the magnitude and 

 period of the inequality is called an 

 equation. An equation of this kind is 

 said to be periodic, when the motions it 

 expresses perform their changes in a 

 comparatively short period of time ; secu- 

 lar, when the changes are so gradual as 

 to be insensible only after the lapse of 

 centuries. Thus, the lunar evection is a 

 periodic, the acceleration of the moon's 

 mean motion, a secular inequality. 



SECULAR REFRIGERATION {sa- 

 culum, an age). The periodical cooling 

 and consolidation of the globe from a 

 supposed original state of fluidity from 

 heat. 



SECUNDINE. The name given by 

 botanists to that sac of the ovule which 

 reposes immediately upon the primine, 

 and often contracts an adhesion with it, 

 so that the two integuments become con- 

 founded. Its point is usually protruded 

 beyond the foramen of the primine. 



SEDIMENTARY ROCKS. Rocks 

 which have been formed by their mate- 

 rials having been thrown down from a 

 state of suspension or solution in water. 



SEED OF PLANTS. The seed of a 

 plant is the ovule in its matured state ; 

 \ it is then a body, enclosed in a pericarp, 

 OG 



