Aether and Gravitation

by William George Hooper

3rd. To every action there is always an equal and contrary reaction.

Corollary.--To these must be added the first Corollary of the three laws which is commonly known as the Parallelogram of Forces, which is as follows: “That when a body is acted upon by two Forces at the same time, it will describe a diagonal, by the motion resulting from their composition, in the same time that it would describe the sides of the parallelogram.”

Now let us apply Newton's Rules of Philosophy to these laws, and see if they fulfil the conditions laid down therein.

In the first place, there being three laws necessary to cover all the motions involved, there is not that simplicity of conception which is a primary factor in the making of any hypothesis. Then it will be observed that even after postulating the three laws, Newton was unable to account for the elliptic orbits of the planets, until he had added a Corollary known as the Parallelogram of Forces.

Art. 13. Force.--The question has arisen also, as to the meaning of the term Force which Newton uses. What is a Force, its cause and mode of operation? The idea of Force is conveyed to us by our “muscular sense,” which gives us the idea of pressure, as for example when we push or pull a body along the ground.

We must not, however, limit our idea of Force to that narrow circle. It has now been fully established that Sound and Heat, Light, Magnetism, and Electricity are Forces, and therefore capable of doing work, as will be shown later on. Newton's use of the term Force is therefore somewhat vague; he does not definitely say what the Force is which causes the change of position, of the body, or of the rate of motion of that body. That it is something to do with Gravitation is obvious, but its exact nature or character is not revealed.

Since Newton's time we have made an advance in the definition of Force, and have come to consider Force as a kind of energy; the application of Force being the application of energy. Such terms as Mechanical Force, Chemical Force, Vital Force, are therefore out of date, and in their place the more definite ideas of energy are substituted. Instead, therefore, of getting such terms as Transformation of Forces, we now get Transformations of Energy. In the chapter on Energy, I hope to show that even that is not a satisfactory solution of the definition of a Force. If we are to make our Philosophy agree with our experience, then Force is due to motion, and motion alone.

So that Centrifugal Force will imply a motion from the centre; Centripetal Force a motion whose effect is ever towards the centre of gravity of any body.

Art. 14. First Law of Motion.--This may naturally be divided into two parts for the purpose of applying the Rules of Philosophy.

(I) Every body continues in a state of rest, except in so far as it is compelled by impressed Forces to change that state. To what extent is this statement conformable to our experience and observation? If I place a body, as for example a weight, on a table, will it remain in that state until it is moved by some other Force? I think that it will so remain, and to that extent the law conforms to experiment.