We may believe what goes beyond our experience, only when it is inferred from that experience by the assumption that what we do not know is like what… - William Kingdon Clifford

In March 1879 Clifford died at Madeira; six years afterwards a posthumous work is for the first time placed before the public. ...The original work as planned by Clifford was to have been entitled The First Principles of the Mathematical Sciences Explained to the Non-Mathematical, and to have contained six chapters, on Number, Space, Quantity, Position, Motion, and Mass respectively. Of the projected work Clifford in the year 1875 dictated the chapters on Number and Space completely, the first portion of the chapter on Quantity, and somewhat later nearly the entire chapter on Motion. The first two chapters were afterwards seen by him in proof, but never finally revised. Shortly before his death he expressed a wish that the book should only be published after very careful revision and that its title should be changed to The Common Sense of the Exact Sciences.

General Results.—Force is a quality of position, definite in magnitude and direction at any point; not constant.
Energy is the name of two different quantities.
1. Energy of motion, half the rate at which a body carries momentum.
2. Energy of position, defined by the statement of the law that the work done in getting from one position to another is the same by whatever path the change of position is made.

I hold in fact
(1) That small portions of space are in fact of a nature analogous to little hills on a surface which is on the average flat; namely, that the ordinary laws of geometry are not valid in them.
(2) That this property of being curved or distorted is continually being passed on from one portion of space to another after the manner of a wave.
(3) That this variation of the curvature of space is what really happens in that phenomenon which we call the motion of matter, whether ponderable or etherial.
(4) That in the physical world nothing else takes place but this variation, subject possibly to the law of continuity.