Air. Aerology no. 7: 1, Free-air data at Drexel, Nebr., and Ellendale, N. Dak., aerological stations, Jan.-Mar. 1918, by Aerological Division, Willis Ray Gregg, in charge; 2, Free-air temperatures during cold winter of 1917-18, by Willis Ray Gregg; 3, Ellendale aerological station, by Vincent E. Jakl.