Elements of Dynamic

Elements of Dynamic is a book published by William Kingdon Clifford in 1878. In 1887 it was supplemented by a fourth part and an appendix. The subtitle is "An introduction to motion and rest in solid and fluid bodies". It was reviewed positively, has remained a standard reference since its appearance, and is now available online as a Historical Math Monograph from Cornell University.

On page 95 Clifford deconstructed the quaternion product of William Rowan Hamilton into two separate products of two vectors: vector product and scalar product. This separation of the quaternion product into two was followed by J. W. Gibbs in his development of vector analysis, first in a pamphlet acknowledging Clifford's Kinematic,^[1] and later in a textbook published by Yale University, called Vector Analysis.

Elements of Dynamic was the debut of the term cross-ratio for a four-argument function frequently used in geometry.

Clifford uses the term twist to discuss (pages 126 to 131) the screw theory that had recently been introduced by Robert Stawell Ball.