The Dome Effect in GOF

[gelite67]

No: HPFGUIDX 152537

When Harry's wand locked with LV's wand in the graveyard, they 
produced a golden, dome shaped web that separated Harry and LV from 
the DEs.

LV then orders the DEs to "do nothing."

Several things I've never understood about this scene.

First, was this "dome effect" part of the Priori Incantatem b/c Harry 
and LV?  The effect itself was only described as "rare" and as 
forcing one of the wands to reveal the brother wand's prior spells. 
Nothing about any protective domes. 

Second, if this is part of the PI effect, was is unique to Harry and 
LV or would it have occurred b/w any two wizards whose wands came 
from the same phoenix?  And by the same phoenix, I don't mean Fawkes, 
I just mean any "same" phoenix?  

Third, if the dome effect is not part of the PI spell, then what 
caused it?  It's clearly related to Fawkes b/c Harry heard/felt the 
phoenix's song emanating from the dome.  He felt the song inside of  
him, which he connected with DD, and felt as though a friend was 
whispering in his ear, "Don't break the connection."  GOF, U.S 
softcover at 664.

I tend to think that this was not a normal part of the PI effect, but 
was an additional effect that was only activated because the PI 
effect betweem Harry's wand and LV's wand was activated.  It seems to 
be part of the "mysterious" protection that always seems to favor 
Harry, but what caused it?  Perhaps something Ollivander did to the 
brother wand after he saw what Tom Riddle had become???  When Harry 
explains to DD and Sirius what happened in the graveyard and DD 
explains the PI to Harry, DD mentions nothing about the protective 
dome, which suggests that DD isn't surprised about it.  

Finally, could the DEs have done anything if LV had wanted them too?  
I don't think they could have, but I don't really have anything to 
support that, other than the protection of the dome would have been 
pretty futile of it could have been broken from the outside.

Angie (wishing everyone a happy Saturday)