THE technicalities' of aviation are becoming news. People want to know .how flying is done ; what raises an aeroplane into the air and keeps it there, and what principles arc invoked to make it easy to control. These first elements of aeronautics Dr. Ivor B. Hart , who is one of the Education Officers of the Air Ministry, will explain in his series of talks, starting today with a resumé of man's early attempts to achieve flight, and a short discussion of the essential problem—force and its effects.