Our inquiry into the nature of things is subject to certain limitations which it is important to realise. The best comparison I can offer is with a future antiquarian investigation, which may be dated about the year 5000 A.D. An interesting find has been made relating to a vanished civilisation which flourished about the twentieth century, namely a volume containing a large number of games of chess, written out in the obscure symbolism usually adopted for that purpose. The antiquarians, to whom the game was hitherto unknown, manage to discover certain uniformities; and by long research they at last succeed in establishing beyond doubt the nature of the moves and rules of the game. But it is obvious that no amount of study of the volume will reveal the true nature either of the participants in the game—the chessmen—or the field of the game—the chess board. With regard to the former, all that is possible is to give arbitrary names distinguishing the chessmen according to their properties; but with regard to the chess-board something more can be stated. The material of the board is unknown, so too are the shapes of the meshes—whether squares or diamonds; but it is ascertainable that the different points of the field are connected with one another by relations of two-dimensional order, and a large number of hypothetical types of chess-board satisfying these relations of order can be constructed. In spite of these gaps in their knowledge, our antiquarians may fairly claim that they thoroughly understand the game of chess.
The application of this analogy is as follows. The recorded games are our physical experiments. The rules of the game, ascertained by study of them, are the laws of physics. The hypothetical chess-board of 64 squares is the space and time of some particular observer or player; whilst the more general relations of two-fold order, are the absolute relations of order in space-time which we have been studying. The chessmen are the entities of physics—electrons, particles, or point-events; and the range of movement may perhaps be compared to the fields of relation radiating from them—electric and gravitational fields, or intervals. By no amount of study of the experiments can the absolute nature or appearance of these participants be deduced; nor is this knowledge relevant, for without it we may
