The prefix <circum> sometimes bears the main stress of the word and sometimes a secondary stress.
Examples of main stress:
ˈcircumcise ˈcircumflex ˈcircumspect ˈcircumstance
The final syllable of circumstance can be stæns, or stɑːns or stəns.
Examples of secondary stress:
ˌcircumloˈcution ˌcircumˈspection ˌcircumˈstantial
The word circumference is an oddity because it is pronounced səˈkʌmfərəns.
2013_10_09