All 3 Uses of

principle
in
Frankenstein - 1831 version

If, instead of this remark, my father had taken the pains to explain to me that the principles of Agrippa had been entirely exploded and that a modern system of science had been introduced which possessed much greater powers than the ancient, because the powers of the latter were chimerical, while those of the former were real and practical, under such circumstances I should certainly have thrown Agrippa aside and have contented my imagination, warmed as it was, by returning with greater ardour to my former studies.†
p. 40.9

principles = basic rules or beliefs

Whence, I often asked myself, did the principle of life proceed?†
p. 52.5 *

principle = basic rule or belief

He appeared at one time a mere scion of the evil principle and at another as all that can be conceived of noble and godlike.†
p. 122.6

Definitions:

(1) (principle)
a basic rule or belief
The exact meaning of principle can depend upon its context. For example:
- "our guiding principles" -- basic moral beliefs that guide decisions and behavior
- "electromagnetic principles" -- rules describing how the world works
- "She lacks principles." -- lacks moral guidelines
- "We agree in principle." -- about important basic beliefs
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

See a comprehensive dictionary for more specialized senses including one in chemistry.