All 3 Uses

principle
in
The Wide Window
(Auto-generated)

Because as soon as Violet saw the flickering reflection, she remembered the scientific principles of the convergence and refraction of light.†
p. 150.6 *

principles = basic rules or beliefs
The scientific principles of the convergence and refraction of light are very confusing, and quite frankly I can't make head or tail of them, even when my friend Dr. Lorenz explains them to me.†
p. 150.6
It's the scientific principles of the convergence and refraction of light!†
p. 153.8

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