wondrous power
The "wondrous power" is magnetism.
Mary Shelley, working within the accepted scientific discourse of her
time, in this second paragraph of her novel, is carefully establishing a
conceptual -- the term in her time would have been "philosophical" -- base
for it in physics. The key is provided by Percy Bysshe Shelley's
citation, in the opening sentence of the Preface, of Erasmus Darwin, a linkage to which the
reader may turn for further elucidation of the scientific grounding of the
novel.
