What's the purpose of the resistor in this circuit?
avishvak: I request you to look at it differently from all the other posts.
This resistor is a constant current sink. Albit a mediocre one. but its just a penny [a paisa in india] 
This thermister needs to sink a constant current in order to produce a temperature dependent voltage at its bottom leg. Normally, about a milliamp does the trick.A resistor is a meiocre surrent sink because its own voltage drop is current dependent. 
these would be better choices [lot more expensive, but hugely more accurate] 
http://octopart.com/search?q=constant+current+sinkavishak, new delhi india