A "wind harp" is a string instrument by which the strings are played by the wind and not by human hand. "Classical wind harps" are boxed shaped instruments made of wood. The strings are positioned closely above the sound layer. Some of these instruments have a wind channel. This channel increases the airflow on wind harps which hang in windows. It's the draught in the house what makes the strings sound. This was popular in England about a hundred years ago. Modern "electronic wind harps" use an electromagnetic pickup and an amplifier. This makes it possible to hear an imperceptible sound on a normal level. When making the strings vibrate by the wind there is not just one tone created, but a lot of overtones. All these tones generate a mystic sound which reminds of the "singing of ghosts".   

The wind plays without any emotion, it needs no pathos,
it doesn't express anything and it needs no rules.
The music of the wind is timeless.
The wind doesn't compel anyone to have any thoughts what soever.
I hear my own music in its music.
The wind is free and it leaves the listener free.

Floating out from the strings;
Whispering in my ear,
The spirit of sound in harmony,
The spirit of the world emerges.
"I am the one who made nature take
Form and instilled it with the
Magic of kindness."

Johann Gottfried Herder

But suddenly,
As the Wind begins to rise,
The fair cry of the harp
Again, to my surprise,
Suddenly makes my soul move.

Eduard Mörike