Access of undefined property instance1

if i create a new sprite/ or a movieclip and then add it to the stage:

var someName:Sprite = new Sprite();
addChild(someName);

that sprite/moviclip is going to have some instance name like “instance1”

i can see that with trace:
trace(someName.name);

but if i then say:
instance1.x = 100;

i wil get an error: “Access of undefined property instance1”

i know i can say:
someName.x = 100;

but why cant i get to it through its instance name, or can i somehow?
and what is the point of that instance name then?

the reason i am asking is if i have multiple sprites with the same name, but different instance names how could i get to each of them in that case?