How does the transistor work in this circuit

[gsingh2011]

In the circuit attached, when S1 is down, a sound is emitted from the speaker. When S3 is down(connected) a lower pitched sound is heard. When S3 is up and S1 is up, a high pitched sound is heard. I don't understand why the pitch changes in those settings, and I also don't understand the purpose of the transistor in the circuit. Why does it need to be there?EDIT: To view the image you have to click on the thumbnail and then click on the image that comes up, which looks black, and then you'll see it. IDK why that's happening..

 

[Studiot]

The transistor is configured as a Hartley Oscillator

http://www.electronics-tutorials.ws/oscillator/hartley.html

The settings of the switches change the tuning capacitor values and thus the frequency of the sound heard.

 

[uart]

Also, I think the transistor should be NPN instead of PNP with the bias voltages in the given circuit.