Possibly the very first jet engine
. Designed by Hero
circa 100 A.D.
, the aeolipile consisted of a boiler
, two tubes extending from the top of the boiler which attached to opposite sides of a metal sphere
, the sphere itself, and two additional bent
tubes attached to the sphere which were left open on the ends.
Fill the boiler with water, light a fire beneath, steam rises up through the tubes attached to the sphere and ultimately escapes through the bent tubes, causing the sphere to spin.
Supposedly, Hero employed this technology in a device which controlled the doors of the local temple.