basicaly the two inductors work as an autotransformer,providing a phase shift of 180 degree
the principle of LC tank ckt. which produces 180 deg phase shift the loop gain AB=1 in hartley oscillator are used 2inductors and 1capacitor
hartley oscillators are mainly used in radio receivers. Also note that due to its wide range of frequencies it is the most popular oscilator
A Colpitts Oscillator is Two Hartley Oscillators http://en.wikipedia.org/wiki/Colpitts_oscillator http://en.wikipedia.org/wiki/Hartley_oscillator ~MECHASUN~
Disadvantages of Hartley OscillatorsThe output is rich in harmonic content and therefore not suitable where a pure sine wave is required.