Page:Truth and Error (1898).djvu/40

 through a series of daily events. It also as a particle changes its position in relation to the sun in a series of annual events. The position of the same body at one time may be related to the position of that body at another time; that is, its space relations may change.

As the motion of one body in its space element may become the measure of the motion of another body in its space elements, so the motion of one body in its time element may become the measure of another body in its time element. While particles are related to one another in number, space and motion, these relations are constantly changing so that they are also related in time; that is, particles are related to each other through their changes. A particle unmodified in its individuality may pass through a succession of changes by reason of its own proper motion determined by the motion of other particles. As the orbit of the moon around the earth may become the measure of the orbit of the earth around the sun, so the day may become the measure of the year. We have now found that numbers, spaces, motions and times are properties which can be measured, and through measurement which is conventional they can be investigated. We shall hereafter see how large a part of the scientific research pursued by man is occupied with these subjects. Quantity is the reciprocal of something else which is usually called quality, but in the course of this discussion it will be found that the term quality is badly chosen, that the real reciprocal of quantity is kind or class.