Norman Robert Campbell

“ Now those propositions state that the mass of a body is independent of its state of motion. When it is deduced from the equations of electromagnetism that the mass of a charged body varies with its motion, the propositions of dynamics are denied to be true, and, accordingly, the term "Absolute Motion" is deprived of all significance. It is logically impossible to assert at the same time (1) that axes fixed in the æther are axes of which the Absolute Velocity is nil, and (2) that the mass of a body increases with its velocity relative to these axes. ”

“ They talked of "reconciling" the results of aberration and of the Michelson experiment; but there was no "reconciliation" needed. The results formed a perfectly logical whole without, any trace of contradiction. It is true that, if velocity is defined as for a solid material body, a conclusion that one body has several different velocities relative! to another does prove that there has been some fallacy in the argument; but they had defined velocity in a perfectly different way, and there was no reason to suppose that the new definition of velocity would have the same limitations as the old. ”

“ The only meaning which is given to the word "velocity" in scientific discussion, which can be stated without assuming the truth of a scientific theory, is , where and are Distances and Times bearing relation A to distances and times. Other quantities, like Absolute Velocity, which are called velocities because they are related in a certain way to Relative Velocities, can only be defined by stating the relation in the form of an equation, which is, in fact, the expression of a scientific theory. ”

“ It is clear at once that if it be not permitted to identify a point in the æther by the energy localized at it, no other means of identification can be substituted. All optical phenomena prove that the æther (outside material bodies) is perfectly homogeneous, so far as the power to contain energy is concerned; the velocity of radiation is rectilinear and uniform in whatever direction it is propagated. All portions of the æther which contain the same amount of energy are, so far as experiment can tell, perfectly similar, and there is no possible means of distinguishing between them ”

“ If both sides could be induced to express their views in detail, the difference between them would be found to concern the fundamental principles of scientific knowledge rather than more special problems of observation and intuition. Perhaps it is because men of science exhibit considerable shyness in discussing the essential foundations of their study that there has been so little direct attack on or defence of the conception of the æther. ”

“ The development of the electromagnetic theory of light has led to the belief that the energy of radiation is essentially of the same nature as that which is localized around an electrically charged body, at rest or in motion. ”

“ When a body is radiating energy to another at a lower temperature separated from it by a finite distance, there is a finite interval of time during which energy has been lost by the first body and has not been gained by the second; if the energy is not to be regarded as lost altogether for that interval, it might seem that it must be regarded as gained by some third body which is neither the source nor the receiver. This body, the body which is the vehicle of the undulatory energy of light, is the æther. ”

“ But, as a matter of fact, in science, as well as in other studies, the propositions are usually historically prior, though logically subsequent, to the definitions. The propositions are chosen for their simplicity, their suitability for mathematical development, or for some such reason, and the first requisite of the definitions of the concepts concerned in the propositions is that they should be such as to make these propositions true. ”

“ I imagine that physicists would agree that it" dynamics could be stated in terms of Relative Motion only, without complicating the equations so that they would be unamenable to mathematical treatment, that course should certainly be adopted. "Absolute Motion" is a disagreeable necessity forced on us by the insufficiency of our powers of mathematical treatment. ”

“ It would be easy to proceed to attack in like manner other confusions to which the use of the concept "æther" has given rise, to analyse the many and mutually inconsistent attempts which have been made to estimate its density, rigidity, and even atomic weight. ”