Th. v. Karman, “ Helicopters,” Aircraft Engineering (1920); M. Luckiesh, Artificial Light, ats Influence on Civilisation (1921); Lichttechnik, ed. by V. A. Fynn, C. G. Ehrenberg (1795- 1876), began to buy heavily in 1916, they had not taken place, office appliances being now provided in the cast, and only those