The difference in pronunciation between the 'th' in various words

this	/ ð /
third	/ θ /
thin	/ θ /
then	/ ð /
three	/ θ /
sympathy	/ θ /
mathematics	/ θ /
mother	/ ð /
another	/ ð /
leather	/ ð /
method	/ θ /
Catholic	/ θ /
rather	/ ð /
southern	/ ð /
clothe	/ ð /
smooth	/ ð /
south	/ θ /
cloth	/ θ /
bathe	/ ð /
bath	/ θ /