In contradistinction to the relativity of the visual angle, classical science considered that the length of the pole itself was absolute, being irrelevant to our relative position as observers. Once again, if we argue as mathematicians, we may claim that this length in turn is relative, since it depends on our measuring conventions. But if we assume that our measuring conventions have been fixed by the requirements of practical congruence, this type of relativity is excluded. Such being the case, classical science believed that the length of the pole was an absolute, inasmuch as its numerical value was so many feet or so many metres regardless of our position and regardless of our motion. It is this last assumption that is contested by Einstein. The absolute magnitude is not the length of the pole; for this, analogously to visual angle, is relative. The absolute magnitude is rather a something which transcends space and time, and relates to the absolute world of space-time. A second illustration may be given by the concepts of mass and weight. As a result of Newton’s discoveries, the weight of a body was realised to be relative, since its value varied with the proximity and distribution of matter. On the earth’s surface the value was so many tons, on the surface of the moon it was considerably reduced, and in interstellar space it vanished completely. A body of itself had no weight. Weight was not immanent in the body; it reduced to the mere expression of a physical relationship between the position of the body and that of surrounding matter. In contradistinction to the relativity of weight, classical science assumed that mass was absolute. The mass of a body, wherever situated and in whatever circumstances observed, was supposed to be an invariant remaining always the same. For this reason, mass, in contrast to weight, was assumed to be immanent in matter. It was not the result of a physical relationship, but was a reflection of the very existence of matter. True, when Bucherer’s experiments had shown that the mass of an electron appeared to increase with its velocity, mass unquestionably [Pg 101] appeared to be relative. But it was assumed that this apparent increase in the mass of the electron was to be ascribed not to any variation in the mass of the electron itself, but to a deformation of its electromagnetic field brought about by motion through the ether. It was as though the ether was dragged along by the electron in its motion, just as a ship moving through the ocean carries along a more or less considerable volume of surrounding water according to the speed with which it is moving. In other words, there had been no real change in the mass of the electron itself, and this belief of classical science was expressed by the principle of the conservation of mass.