Sea. See Ocean.
Seismometer, the, 205.
Seleucus of Erythrea, his astronomical studies, 65.
Seneca, noticed the direction of the tails of comets, 102; his views on the nature and paths of comets, 103, 104; omens drawn from their sudden appearance, 111; the germs of later observations on earthquakes found in his writings, 207; problematical extinction and sinking of Mount Aetna, 227, 240.
Shoals, atmospheric indications of their vicinity, 309.
Sidereal systems, 89, 90.
Siljerstrom, his observations on the Aurora, with Lottin and Bravais, on the coast of Lapland, 195.
Sirowatskoi, "Wood Hills" in New Siberia, 281.
Snow-line of the Himalayas, 30-33, 331, 334; of the Andes, 330; redness of long-fallen snow, 344.
Solar system, general description, 90-154; its position in space, 89; its transistory motion, 145-150.