- § 351. Retrospect
- § 352. Geometry is the science of series of two or more dimensions
- § 353. Non-Euclidean geometry
- § 354. Definition of dimensions
- § 355. Remarks on the definition
- § 356. The definition of dimensions is purely logical
- § 357. Complex numbers and universal algebra
- § 358. Algebraical generalization of number
- § 359. Definition of complex numbers
- § 360. Remarks on the definition

The Principles of Mathematics was written by Bertrand Russell, and published in in 1903. It is now available in the Public Domain.