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Harry had soon mastered the Impediment Curse, a spell to slow down and obstruct attackers; the Reductor Curse, which would enable him to blast solid objects out of his way; and the Four-Point Spell, a useful discovery of Hermione’s that would make his wand point due north, therefore enabling him to check whether he was going in the right direction within the maze.

He supposed he should have known better; the Reductor Curse was for solid objects.

When none appeared, he tried the Reductor Curse again.

This is brought about by the use of a modified Jones reductor, as shown in Figure 1.

This reductor is a standard apparatus and is used in other quantitative processes.