Threads Open To Newest Post

I have looked but can not find a place to set the forum so that when I open a thread it opens to the post that started the thread. It always opens to the newest post. That is great on threads I have been reading but for a thread that has been around a while I would rather it opened at the first post. I know there is a way, but I am too dense to locate it. Anyone have the trick for this? Thanks!
-Spike