SPECIAL ARTICLES.—Solar and sky radiation measurements during Jan. 1918; by Herbert H. Kimball.—Mathematical theory of sound ranging; by Harry Bateman.— Mean values of free-air barometric and vapor pressures, temperatures, and densities over United States; by Willis Ray Gregg.—Turning of winds with altitude; by Willis Kay Gregg.—Air chimneys of ice below waterfall; by Robert R. Horton.—Cyclones, tornadoes, thunderstorms, squalls; by Alfred J. Henry.—Pitfalls of meteorological periodicities; by W. W. Bryant.—Lawrence Hargrave, 1850-1915; by R. Greig-Smith.