In March 1879 Clifford died at Madeira; six years afterwards a posthumous work is for the first time placed before the public. Some explanation of this delay must be attempted in the present preface.
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.
Upon Clifford's death the labour of revision and completion was entrusted to Mr E C Eowe, then Professor of Pure Mathematics at University College, London. That Professor Eowe fully appreciated the difficulty and at the same time the importance of the task he had undertaken is very amply evidenced by the time and care he devoted to the matter. Had he lived to complete the labour of editing, the work as a whole would have undoubtedly been better and more worthy of Clifford than it at present stands. On the sad death of Professor Eowe, in October 1884, I was requested by Messrs Kegan Paul, Trench, & Co. to take up the task of editing, thus left incomplete. It was with no light heart, but with a grave sense of responsibility that I undertook to see through the press the labour of two men for whom I held the highest scientific admiration and personal respect. The reader will perhaps appreciate my difficulties better when I mention the exact state of the work when it came into my hands. Chapters I. and II, Space and Number; half of Chapter III., Quantity (then erroneously termed Chapter IV.); and Chapter V., Motion, were in proof. With these proofs I had only some half-dozen pages of the corresponding manuscript, all the rest having unfortunately been considered of no further use, and accordingly destroyed. How far the contents of the later proofs may have represented what Clifford dictated I have had no means of judging except from the few pages of manuscript in my possession. In revising the proofs of the first two chapters, which Clifford himself had seen, I have made as little alteration as possible, only adding an occasional foot-note where it seemed necessary. From page 65 onwards, however, I am, with three exceptions in Chapter V., responsible for all the figures in the book.
After examining the work as it was placed in my hands, and consulting Mrs. Clifford, I came to the conclusion that the chapter on Quantity had been misplaced, and that the real gaps in the work were from the middle of Chapter III. to Chapter V., and again at the end of Chapter V. As to the manner in which these gaps were to be filled I had no definite information whatever; only after my work had been completed was an early plan of Clifford's for the book discovered. It came too late to be of use, but it at least confirmed our rearrangement of the chapters.
For the latter half of Chapter III. and for the whole of Chapter IV. (pp. 116-226) I am alone responsible. Yet whatever there is in them of value I owe to Clifford; whatever is feeble or obscure is my own.
With Chapter V. my task has been by no means light. It was written at a time when Clifford was much occupied with his theory of "Graphs," and found it impossible to concentrate his mind on anything else: parts of it are clear and succinct, parts were such as the author would never have allowed to go to press. I felt it impossible to rewrite the whole without depriving the work of its right to be called Clifford's, and yet at the same time it was absolutely necessary to make considerable changes. Hence it is that my revision of this chapter has been much more extensive than in the case of the first two. With the result I fear many will be dissatisfied; they will, however, hardly be more conscious of its deficiencies than I am. I can but plead the conditions under which I have had to work. One word more as to this chapter. Without any notice of mass or force it seemed impossible to close a discussion on motion; something I felt must be added. I have accordingly introduced a few pages on the laws of motion. I have since found that Clifford intended to write a concluding chapter on mass. How to express the laws of motion in a form of which Clifford would have approved was indeed an insoluble riddle to me, because I was unaware of his having written anything on the subject. I have accordingly expressed, although with great hesitation, my own views on the subject; these may be concisely described as a strong desire to see the terms matter and force, together with the ideas associated with them, entirely removed from scientific terminology - to reduce, in fact, all dynamic to kinematic. I should hardly have ventured to put forward these views had I not recently discovered that they have (allowing for certain minor differences) the weighty authority of Professor Mach, of Prag. But since writing these pages I have also been referred to a discourse delivered by Clifford at the Royal Institution in 1873, some account of which appeared in Nature, June 10, 1880. Therein it is stated that "no mathematician can give any meaning to the language about matter, force, inertia used in current text-books of mechanics." This fragmentary account of the discourse undoubtedly proves that Clifford held on the categories of matter and force as clear and original ideas as on all subjects of which he has treated; only, alas! they have not been preserved.