The aim of research is the discovery of the equations which subsist between the elements of phenomena. The equation of an ellipse expresses the universal _conceivable_ relation between its co-ordinates, of which only the real values have _geometrical_ significance. Similarly, the equations between the elements of _phenomena_ express a universal, mathematically conceivable relation. Here, however, for many values only certain directions of change are _physically_ admissible. As in the ellipse only certain _values_ satisfying the equation are realised, so in the physical world only certain _changes_ of value occur. Bodies are always accelerated towards the earth. Differences of temperature, left to themselves, always grow less; and so on. Similarly, with respect to space, mathematical and physiological researches have shown that the space of experience is simply an _actual_ case of many conceivable cases, about whose peculiar properties experience alone can instruct us. The elucidation which this idea diffuses cannot be questioned, despite the absurd uses to which it has been put. Let us endeavor now to summarise the results of our survey. In the economical schematism of science lie both its strength and its weakness. Facts are always represented at a sacrifice of completeness and never with greater precision than fits the needs of the moment. The incongruence between thought and experience, therefore, will continue to subsist as long as the two pursue their course side by side; but it will be continually diminished. In reality, the point involved is always the completion of some partial experience; the derivation of one portion of a phenomenon from some other. In this act our ideas must be based directly upon sensations. We call this measuring.[67] The condition of science, both in its origin and in its application, is a _great relative stability_ of our environment. What it teaches us is interdependence. Absolute forecasts, consequently, have no significance in science. With great changes in celestial space we should lose our co-ordinate systems of space and time.