Air Sacs

Prolongations of the lungs of birds into different parts of the body cavity, as the interclavicular, thoracic, and abdominal; also into the bones. Analogous expansions of the tracheal breathing apparatus of insects are terined air vesicles. Air-Ship. Much experimentation and considerable progre has been made toward air-transportation, but no navigable balloon, flying or other air-machine has yet been perfected which is sufficiently reliable to effect the revolution of warfare, which such an accomplishment would cause. Maxim's flying machine is the most promising of the many tried: the French balloon, "La France," has attained a speed of 15 m. an hour under favorable atmospheric conditions.