William Kingdon Clifford Quotes

Energy [is of two kinds: 1. Energy of motion; 2. Energy of position].

Force, defined as above, is not conserved at all. It may appear and disappear; it is continually being created and destroyed. "Conservation of force" is, mathematically speaking, a contradiction in terms.

Force cannot be explained without stating a law of nature concerning momentum, viz.:—
Suppose a body with a certain momentum to be the only body in the universe; it will go on with the same momentum.
The case of bodies in contact is no exception to this law, but only a particular case. Here the change of motion is called pressure. The case of bodies not in contact is illustrated by the motion of the earth about the sun [under the force of gravitation, as we call it].
In all cases change of motion is connected by invariable laws with the position of surrounding bodies. Force, then, has a definite direction [at every instant] at any point in space, and depends on the position of surrounding bodies, and may be described as the change of momentum of a body considered as depending upon its position relative to other things. It embodies the quality of direction as well as magnitude. In other words, it is a quantity having direction.

may be roughly described as quantity motion. A body moving at a speed of say twenty an hour, has a certain quantity of motion. If the body goes forty miles an hour there is twice as motion; or if twice as much matter goes twenty miles hour, there is also twice as much motion. Momentum is measured by the quantity of matter moving at a rate mass <math>\times</math> velocity.

Causation is defined by some modern philosophers as unconditional uniformity of succession, e.g., existence of fire follows from putting a lighted match to the fuel.
This idea must be got rid of to understand force. All universally true laws of nature are laws of co-existence, not succession. ...In every case the law at work is seen to be a law of co-existence, not succession.

No mathematician can give any meaning to language about matter, force, inertia, used in text-books of mechanics.

Remember, then, that [scientific thought] is the guide of action; that the truth which it arrives at is not that which we can ideally contemplate without error, but that which we may act upon without fear; and you cannot fail to see that scientific thought is not an accompaniment or condition of human progress, but human progress itself. And for this reason the question what its characters are... is the question of all questions for the human race.

I specially wish you not to go away with the idea that the exercise of scientific thought is properly confined... When the Roman jurists applied their experience of Roman citizens to dealings between citizens and aliens, showing by the difference of their actions that they regarded the circumstances as essentially different, they laid the foundations of that great structure which has guided the social progress of Europe. That procedure was an instance of strictly scientific thought. When a poet finds that he has to move a strange new world which his predecessors have not moved; when, nevertheless, he catches fire from their flashes, arms from their armoury, sustentation from their foot-prints, the procedure by which he applies old experience to new circumstances is nothing greater or less than scientific thought. When the moralist studying the conditions of society and the ideas of right and wrong which have come down to us from a time when war was the normal condition of man and success in war the only chance of survival, evolves from them the conditions and ideas which must accompany a time of peace, when the comradeship of equals is the condition of national success; the process by which he does this is scientific thought and nothing else.

By scientific thought we mean the application of past experience to new circumstances by means of an observed order of events. By saying that this order of events is exact we mean that it is exact enough to correct experiments by, but we do not mean that it is theoretically or absolutely exact, because we do not know. The process of inference [is] in itself an assumption of uniformity, and... as the known exactness of the uniformity became greater, the stringency of the inference [is] increased. By saying that the order of events is reasonable we do not mean that everything has a purpose, or that everything can be explained, or that everything has a cause; for neither of these is true. But we mean that to every reasonable question there is an intelligible answer, which either we or posterity may know by the exercise of scientific thought.

I am endeavouring in a general way to explain the laws of double refraction on this hypothesis, but have not yet arrived at any results sufficiently decisive to be communicated.

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.

Riemann has shewn that as there are different kinds of lines and surfaces, so there are different kinds of space of three dimensions; and that we can only find out by experience to which of these kinds the space in which we live belongs. In particular, the axioms of plane geometry are true within the limits of experiment on the surface of a sheet of paper, and yet we know that the sheet is really covered with a number of small ridges and furrows, upon which (the total curvature not being zero) these axioms are not true. Similarly, he says although the axioms of solid geometry are true within the limits of experiment for finite portions of our space, yet we have no reason to conclude that they are true for very small portions; and if any help can be got thereby for the explanation of physical phenomena, we may have reason to conclude that they are not true for very small portions of space.

The name philosopher, which meant originally 'lover of wisdom,' has come in some strange way to mean a man who thinks it is his business to explain everything in a certain number of large books. It will be found, I think, that in proportion to his colossal ignorance is the perfection and symmetry of the system which he sets up; because it is so much easier to put an empty room tidy than a full one.

There is in the true man of science a desire stronger than the wish to have his beliefs upheld; namely, the desire to have them true.

We ought not to teach to little children, as a known fact, that which is not a known fact.