SECOND—One-sixtieth of a minute: 1-3600 of a mean solar hour. SECONDARY COMPENSATION—Same as "auxiliary compensation." See _Auxiliary_. SECONDS HAND—The hand on the dial of a clock or watch which revolves once a minute. Sometimes small and set in a small circle of its own. Sometimes long and traverses the whole dial. See _Center-seconds and Sweep-seconds_. SECONDS PIVOT—The prolongation of the fourth wheel arbor to which the seconds hand of a watch is fixed. SECONDS, SPLIT—Divided seconds—into quarters, or fifths; measured by a chronograph. SHADOW—A darkened space resulting from the interception of light by an opaque body. SHAGREEN—Made from the tough skin that covers the crupper of a horse or ass. Rough seeds are trodden into the skin and then allowed to dry. The seeds are shaken out and the skin dyed green. Then the rough surface is rubbed down smooth leaving white spots on the green ground. Also made from the rough skin of sharks and dolphins. Formerly used a great deal for the outer cases of watches. See _Pair Cases_. SHERWOOD, NAPOLEON BONAPARTE—Born in 1823. About 1855 he entered the watchmaking business in the employ of the Waltham Watch Co. He revolutionized jeweling methods and invented among other things a "Counter-sinker," "End-shake tools," "Truing-up tools" and "Opener." In 1864 he organized the Newark Watch Company but within a few months severed his connection with it. He died in 1872. SIDEREAL TIME—The standard used by astronomers; measured by the diurnal rotation of the earth, which turns on its axis in 23 hours, 56 minutes, 4.1 seconds. The sidereal day is therefore 3 minutes, 56 seconds shorter than the mean solar day. Mean time clocks can be regulated with greater facility by the stars than by the sun for the motion of the earth with regard to the fixed stars is uniform. Clocks all over the United States are so regulated from the Naval Observatory at Washington. SIDE-SHAKE—Freedom of pivots to move sideways. See _End-Shake_. SLOW TRAIN—A train whose balance vibrates 14,400 times an hour. Now never used in pocket watches because of susceptibility to inequalities in the pull of the mainspring, jars, sudden movements, etc. Used, however, in marine chronometers. SNAIL—A cam shaped like a snail, used generally for gradually lifting and suddenly discharging a lever, as in the striking mechanism of clocks. SNAILING—A method of ornamenting with circles and bars parts of a watch movement which it is not desirable to polish highly. SOLAR TIME—Time marked by the diurnal revolution of the earth with regard to the sun, of which the midday is the instant at which the sun appears at its greatest height above the horizon. This instant varies from twelve o'clock mean time because the earth also advances in its orbit and its meridians are not perpendicular to the ecliptic.