CHAPTER XXI.

THEORY OF APPROXIMATION.

1. Theory of Approximation 456

2. Substitution of Simple Hypotheses 458

3. Approximation to Exact Laws 462

4. Successive Approximations to Natural Conditions 465

5. Discovery of Hypothetically Simple Laws 470

6. Mathematical Principles of Approximation 471

7. Approximate Independence of Small Effects 475

8. Four Meanings of Equality 479

9. Arithmetic of Approximate Quantities 481