Physical science, it must be remembered, deals with a common objective world. This world is not apprehended directly, but issues from a long, laborious, ever-widening synthesis of private views. Primarily, all we are aware of is a complex of sensations. Even the crude knowledge of the savage is therefore itself the result of a highly complex synthesis. But science must pursue the synthesis still farther, taking the results of previous syntheses as the elements of its more sophisticated ones. And so what was formerly the synthetic view becomes the private one when we rise to a higher plane. Thus, if we consider the aspect of the earth’s surface, viewed from any one spot, our private view would suggest that the earth was flat. Only a synthesis of a number of private views and experiences can lead us to assert that the earth is round; and science accordingly speaks of the rotundity of our planet and ignores its flatness. To put it in more technical language, the search for the objective world is similar to that of the search for the invariants or invariant equations of a group of transformations. In this illustration, each transformation corresponds to the passage from one private perspective to another, whereas the invariants correspond to the entities of the objective world with which science deals. The discovery of the space-time universe, to be discussed in a future chapter, illustrates the procedure. To be sure, in many instances the private view may be of greater interest than the collective one. This will be the case if an artist wishes to paint a landscape on his canvas. He will, of course, draw distant objects on a smaller scale and make the rails converge. But, in contradistinction to the artist, the scientist is not particularly interested in the private view except as a means to an end. His ultimate goal is the common objective world.