Horace Walpole uses the motif of portable lights at several points in The Castle of Otranto to signal the incomplete, confusing or partial understanding of something by a character. For example, in Chapter 1 when Manfred is trying to prevent Isabella from escaping the Castle, Walpole writes:
The noise of the falling door had been heard by Manfred, who, directed by the sound, hastened thither, attended by his servants with torches. “It must be Isabella,” cried Manfred, before he entered the vault; “she is escaping by the subterraneous passage, but she cannot have got far.” What was the astonishment of the prince, when, instead of Isabella, the light of the torches discovered to him the young peasant, whom he thought confined under the fatal helmet!
The light of the torches, which only spreads where it is directed, represents partial vision and understanding. Because the torches are always being carried by a human character, its illumination only goes where they want to bring it. Torchlight or lamplight signals the limitations of human understanding and of each character's single perspective in The Castle of Otranto. No one's "torch" or "lamp" can show everything that's happening at once.
Nonetheless, although the direction of the light is controlled by humans, the light itself seems to act almost independently. Once something is lit up, Walpole implies, it cannot be unseen. For example, in the above passage the light of the torch "discovers to" Manfred a truth he is not expecting, even though he is the one holding the flame.
When Isabella is trying to escape the castle, she also brings a portable light source with her. Even so, the lamp doesn't do much to assuage her fears. She is still terrified by the darkness and can only see what is directly ahead of her. In comparison to Manfred, who is carrying fire, this gentler light reflects the relative softness of Isabella's character. While Manfred burns, Isabella glows.
The limitations of portable lights make illumination from natural sources seem even more revelatory, as they cannot be controlled by humans and thus show everything indiscriminately. Moonlight, or "moonshine" for instance, reveals disturbing truths to Manfred at very inconvenient moments for him. When he is holding a torch, he retains a bit of control, but he can't fight the moonlight.
The Castle of Otranto is split up by lots of narrow passageways and hallways, and descriptions of these recur as motifs from the beginning of the book until the end. In Chapter 1, when Isabella escapes from Manfred's sexual advances, she decides she will use a secret passage in the twisting underbelly of the castle as her exit:
In this resolution, she seized a lamp, that burned at the foot of the staircase, and hurried towards the secret passage. The lower part of the castle was hollowed into several intricate cloisters; and it was not easy for one, under so much anxiety, to find the door that opened into the cavern [...] that long labyrinth of darkness.
The descriptions of these corridors and passages are a major contributing factor to the Gothic atmosphere of the novel. Even though the Castle of Otranto is a home, it is not welcoming. Rather, it is an unfriendly and sometimes frightening building, a "labyrinth of darkness" that's difficult to navigate and full of chilling obscurity. The figurative language of silence, darkness, and confusion here makes the reader feel the gloomy, threatening impression that these abandoned chambers have on Isabella. There's a strong contrast between the emotionally heightened scenes that precede this and the "awful silence" that Isabella encounters, as if she has moved from the world of the living to the winding, intricate world of the dead.
The natural world of The Castle of Otranto is as tumultuous as the events going on inside the castle's walls, and Walpole uses the motif of a thunderstorm at three important points in the book to illustrate this. For example, in Chapter 5, a mighty vision of Alfonso appears to announce the true heir to Otranto, and this vision is accompanied by thunder:
[...] a clap of thunder, at that instant, shook the castle to its foundations; the earth rocked, and the clank of more than mortal armour was heard behind. [...] The moment Theodore appeared, the walls of the castle behind Manfred were thrown down with a mighty force, and the form of Alfonso, dilated to an immense magnitude, appeared in the centre of the ruins. “Behold in Theodore the true heir of Alfonso!” said the vision: and having pronounced these words, accompanied by a clap of thunder, it ascended solemnly towards Heaven [...]
The sounds of thunder in this book are related to dramatic revelation, and they occur primarily in events surrounding Theodore, the true heir to Otranto. The noise and the force of the thunder are extremely powerful, as they "rock" the earth and have "mighty" impacts, making the reader feel the full weight of their booming interruptions. These cacophonous sounds from the natural world work to support Theodore's position as the "natural heir" to Otranto. Even the thunder knows it shouldn't be Manfred in the prince's chair.
Thunder and lightning are associated with visitations from God in the Christian tradition, and so when they occur in The Castle of Otranto, they also signal divine intervention. Each time thunder is heard in the novel, they signify important events involving Theodore's right to his true title. After the first instance, which shakes the castle "to its foundations," these thunder claps then occur when Theodore is released from prison by Matilda and also when she dies, provoking Theodore's return to the castle. The "clapping" of the thunder punctuates the entrance and exit of the ancestral spirit here very dramatically. They silence everything else and ensure that all attention is focused on the ghost of Alfonso and his important message.
