What interest fascinates Victor?

Victor is fascinated by natural philosophy.

Henry Clerval is fascinated by Languages.

Clerval was no natural philosopher. His imagination was too vivid for the minutiae of science. Languages were his principal study; and he sought, but acquiring their elements, to open a field for self-instruction on his return to Geneva. Persian, Arabic, and Hebrew, gained his attention, after he had made himself perfectly master of Greek and Latin.