One Membership Database, two Web Applications

Hi,
I'm running a SQL 2008 Database with Membership Structure.
My two web-Applications are both connected to this Database and are using same User-Pool. So I can login with my user to the one or the other.
My question: when a user login at web-Application 1, how can I provide, that the user, when he goes to Web-Application 2, is automatically loged in there, too? 
 
Greetings
 
 
Tom
 
 
...