You're thanking the Quarters telling them that the ritual is over. An example of a Quarter dismissal might be:

The East, the wind,
The Sylphs, the air,
I thank thee all
For being here.

Again, you can see the various components--you're not ordering them to leave, you're politely telling them that this ritual is over but if they'd like to stick around for tea, they'd be welcome.

For a complete set of Quarter calls and dismissals, check here.