PHP - Overloading

class Settings_Core
{
private function _Global_Settings(){
global $MySQL;
$Query = 'Select `Name`, `Value` From `Site_Settings`.`Global` Where `Active` = 1 Order By `Id` ASC';
$Result = $MySQL->query($Query, MYSQLI_USE_RESULT);
while($Data = mysqli_fetch_assoc($Result)){
$this->Global[$Data['Name']] = $Data['Value'];

}
}
};

error is
Notice: Indirect modification of overloaded property Settings_Co :$Global has no effect in /var/www/Include/Core/Settings.Class.php on line 28

I have no idea what to do or what this means or how to fix it