Mail preview window?

[shaun hayes-holgate]

I hate to bug the list about something so trivial but I hit a button 
while
in Mail and lost the preview window that divides the mail list from the
mail contents.I've looked everywhere in the dropdowns and the Help
menu but can't find a solution to get it back.
First person to reply with the correct answer gets a free email reply
with the words 'Thanks' typed out by hand.And a smiley face thingy.   :}

thanks.