Complex sentence: He was supposedly something of a faddist, believing in animal magnetism as a key to health; but again, his eccentricities are based on what was learned from Adelaide and Dyson, both of whom had reasons to lie.
Split into simpler sentences: He was supposedly something of a faddist, believing in animal magnetism as a key to health. But again his eccentricities are based on what was learned from Adelaide and Dyson, both of whom had reasons to lie.