Dumbledore Protecting the Stone

[mrflynn6]

No: HPFGUIDX 39453

Another thought I have had on why the mirror was in the room was that 
Harry needed to find the mirror and know how it works before he 
incountered Voldermort.  Would Harry have known to lie about what he 
saw in the mirror if he had not known how it works?  If he had come 
upon the mirror for the first time when he saw Voldermort, he might 
have said that he sees the stone or even himself holding the stone 
without knowing how the mirror worked.  

The stone could have been in the mirror the entire time.  Diversion 
is a good thing when trying to fool your enemy.  Snape suspected 
Quirrell which almost insures that Dumbledore knew what he was up 
to.  The annoucement at the beginning of the term was probably meant 
to throw him off the trail of the stone until the time was right.