The accompanying figures illustrate (i) the kind of slice which is included in this law and (ii) the kind of slice which is excluded. Fig. 19. It immediately follows that—with the nomenclature of the enunciation of the law— is located in every oblique cross-section of . If be the time-system of the duration in which is motionless and, in some other time-system , ′ be the duration of maximum extent which intersects in an oblique slice, then throughout ′ in the time-less space of a the material object has a uniform motion of translation with the velocity of in . 58.2 This property, possessed by a material object which is motionless in a time-system , of being situated in every oblique slice of its stationary situation is a fundamental physical law of nature. Namely, percipients cogredient with different time-systems can 'recognise' the same material objects. In other words, the character of a material object is not altered by its motion. 58.3 The motion of a material object is 'regular' when if be any volume in which it is located and be any event-particle in , and ′ be any variable volume which contains and is a portion of , and ′ be the extensive component of which is located in ′, then, as ′ is progressively diminished without limit, a time-system can be found such that the errors of calculations, respecting magnitudes exhibited by ′ which assume that ′ is motionless in , tend to the limit zero, provided that the time-lapse of the durations in within which ′ is motionless is also correspondingly diminished without limit. The above definition of regular motion is a description of the assumptions in the ordinary mathematical treatment of the motion of a material object (not necessarily rigid) which is not moving with a uniform motion of translation. If be the standard time-system to which motions are referred, then the velocity of in is the velocity at the event-particle [i.e. at the -space point at the -time ] of the material object. 59. Extensive Magnitude. 59.1 A theory of extensive magnitude is required to complete the theory of material objects. Let and ′ be two objects (material or otherwise), then the statement that and ′ possess quantities of a certain kind and that the ratio of the quantity to the quantity ′ has a certain definite numerical value is a reference to some determinate method of comparison of to ′ which is the defining characteristic of that kind of quantity[9]. The quantity of a certain kind possessed by a material object is called 'extensive' when it is a determinate function of the quantities of the same kind possessed by any two of its extensive components which (i) are exhaustive of and (ii) are non-overlapping [i.e. have no extensive component in common].