Internal resonance occurs when a writer sets up a motif to a story, and deepens the readers' emotions by playing upon that motif. Let's discuss a couple of examples from Tolkien.

The Lord of the Rings  is a story of loss, a tale of how each of us experiences the wonders and the beauties of the world, and then must leave them behind. Tolkien begins setting us up for this loss right from the beginning. Frodo Baggins is hesitant to leave the Shire when he was supposed to, for he doesn't really want to lose his home, Bag End. Yet he puts it up for sale and makes a big show of leaving, spending many a night to walk its trails in the starlight and say his goodbyes. This almost does him in, for he is nearly captured by the Nine Dark Riders.

Yet he finds refuge from them in the home of Farmer Maggot, and reluctantly says goodbye to a new-found friend.

Then again, the same type of action is repeated in the home of Tom Bombadil.

And once again he finds solace and friendship in Rivendell, and is forced to leave.

Frodo then finds friendship among his traveling companions, but Gandalf is torn from the party in the Mines of Moria, and once again Frodo is forced to flee with his life in danger.

In Lothlorien Frodo takes refuge, and like a man who has been jilted by his lover, he offers his ring to Galadriel. But all too soon he realizes that in order to keep her safe, he has to leave Lothlorien.

Indeed, he decides to leave everyone behind at the end of The Fellowship of the Ring, and races off even as the Orcs attack his friends.

Do you see what Tolkien is doing? At least seven times in one novel, Frodo is forced to escape from places of comfort and refuge. And he leaves behind his refuge a couple more times in the succeeding novels.

Tolkien is of course setting us up for the very end of the novel, that moment where Frodo must sail off into the Grey Havens, leaving behind the world that he loved so dearly, the world that he saved.

Had Tolkien not emphasized how much Frodo (an orphan) longed for a home, that final scene would have had very little impact indeed. Instead, Frodo's final farewell to the Shire is devastating, a real tear-jerker.

But do you see how Tolkien did it? He simply repeated an action over and over again, playing upon variations, trying to make each instance of leaving more powerful and difficult than the last—when appropriate.

Here's another example, a very simple but powerful one. Perhaps one of the most compelling scenes for me was the Fellowship's journey into and through the mines of Moria.

Do you recall the opening to that scene? The group must walk along the edge of a still pool, where the only sound is the occasional sound of dripping water. The very solitude of the place sets them all on edge. One of the Hobbits throws a rock, and moments later the group is attacked by the "watcher" of the lake.

They escape the monster and make it into the Mines of Moria, only to have the door blocked with boulders behind them.

Inside the mine, Frodo cannot sleep that night for the dripping sound of water. (Note the repetition of a single spooky element, made unsettling by the attack of the watcher.) A few nights later, that dripping sound is replaced by the distant sound of a hammer going, tink, tink, clank, tink.

Suddenly, Frodo realizes that he's not alone, and soon he sees the glowing eyes of Gollum in the cave.

Finally, as they near the exit, the "plink" of water, the "tink" of a hammer, is suddenly replaced by the sound of drums in the deep—huge thunderous sounds that roll through the cavern, roaring "Doom! Doom! Doom!"

Here, the internal resonance is simply a repeated sound, one that grows louder, more unsettling, and more menacing with each repetition.

Here's a third use of internal resonance in The Lord of the Rings: the journey through the underworld. We see the first hint of it in the Shire, when the Hobbits escape one of the nine riders by diving off the road. They find themselves in a cave-like overhang while one of the nine riders tries to draw them out, and Frodo imagines himself suddenly to be in a tunnel.

Later, as they leave the Shire, they dive through a hedge—and find themselves in a forest so deep that it seems almost lightless. After leaving Tom Bombadil's house, they take too long on the road, and find themselves suddenly dragged into the lightless burrow of a wight.

They find themselves in another tunnel at the inn at Bree—a hobbit hole, where once again they are attacked by the nine riders.

They make it to Weathertop, and Frodo is stabbed with a magic blade that breaks off—but begins working its way to his heart. As he loses consciousness, he once again imagines himself to be in a tunnel.

The group heads toward Mordor, and along the way our protagonists are forced to take an ill-fated detour through the Mines of Moria.

Frodo and Sam later split off from the group and make their journey to Mordor—having to take Gollum's secret path that will lead through Shelob's lair.

Merry and Pippin mirror that journey as they journey into the Entwood, beneath trees so old and hoary that they block out all light— until Merry and Pippin find themselves given shelter in Treebeard's cave.

Gandalf himself has a lightless journey after falling into the pit in the Mines of Moria. There, he chases the Balrog through endless caverns in an epic duel that is only related as he tells it to the Hobbits.

Meanwhile, Aragorn and the others take their own lightless journeys—fighting the orcs in the caverns at Helm's Deep— until at last Aragorn must take one final journey through a tunnel so that he can summon the spirits of the dead to fight in behalf of Gondor.

And we cannot forget the final lightless journey—Frodo's journey to the Crack of Doom.

Each of these lightless journeys, of course, is a play upon a theme, designed to heighten that final moment when Frodo steps toward the Crack of Doom—and all light fails him.

So, there I've given you three examples of how Tolkien uses internal resonance in The Lord of the Rings in order to heighten his reader's emotions. Perhaps you will find this tool of some value as you plot your own novels.