In Frankenstein, what happens when Victor, at age fifteen, sees an oak tree destroyed by lightning and hears an explanation? What does Victor then...

Victor sees a spectacular proof of the power of the nature when he witnesses lightning strike a tree with "curiosity and delight." He says, 

I beheld a stream of fire issue from an old and beautiful oak [...]; and so soon as the dazzling light vanished, the oak had disappeared, and nothing remained but a blasted stump [....]. It was not splintered by the shock, but entirely reduced to thin ribbands of wood. I never beheld anything so utterly destroyed.

In witnessing the extreme power of the natural world, Victor loses interest in the supernatural. Any interest that he once had in alchemy or searches for the philosopher's stone or the elixir of life dissolves when he sees what is possible with the intensity and dominance of electricity, a natural power that has the force to obliterate a very large and solid oak (a tree known for its own strength).

Victor says that, although he lost interest in the writers who focused on the supernatural and the occult, "by some fatality [he] did not feel inclined to commence the study of any modern system [of science]." Instead, he turned to the study of mathematics and languages (Greek, English, and German) until his parents determined to send him to the university at Ingolstadt when he turned seventeen. It was at the university that Victor began his study of modern science.