8.2 An event-particle occupies instantaneously a certain point in the space of and a certain point in the space of . Thus instantaneously there is a certain correlation between the points of the space of and the points of the space of . Also if the particle has the character of material at rest at the point in the space of , this material-particle has a certain velocity in the space of ; and if it be material at rest at the point in the space of , the material-particle has a certain velocity in the space of . The direction in -space of the velocity due to rest in the correlated -point is said to be opposite to the direction in -space of the velocity due to rest in the correlated -point. Also with congruent units of space and of time, the measures of the velocities are numerically equal. The consequences of these fundamental facts are investigated in Part III. The relation of the -space to the -space which is expressed by the velocities at points in -space due to rest in the points of -space and by the opposite velocities in -space due to rest in the points of -space is called the 'kinematic relation' between the two consentient sets, or between the two spaces. 8.3 The simplest form of this kinematic relation between a pair of consentient sets is when the motion of either set in the space of the other is a uniform translation without acceleration and without rotation. Such a kinematic relation will be called 'simple.' If a consentient group has a simple kinematic relation to each of two consentient sets, and , then and have a simple kinematic relation to each other. In technical logical language a simple kinematic relation is symmetrical and transitive. The whole group of consentient sets with simple kinematic relations to any one consentient set, including that set itself, is called a 'simple' group of consentient sets. The kinematic relation is called 'translatory' when the relative motion does not involve rotation; namely, it is a translation but not necessarily uniform. 8.4 The fact that the relational theory of space involves that each consentient set has its own space with its own peculiar points is ignored in the traditional presentation of physical science. The reason is that the absolute theory of space is not really abandoned, and the relative motion, which is all that can be observed, is treated as the differential effect of two absolute motions.