626 VIII. ON THE STRUCTURE OF MATHEMATICS 

The problem is to determine whether a particular kind of spacetime is possible. We must investigate the different g's which give us different kinds of spacetime, and not those which distinguish different kinds of mesh systems in one spacetime. This means that our formulae must not be altered in any way if we change the mesh system.
The above condition makes an extraordinarily simple test of laws that have been or may be suggested. Among others, Newton's law is swept away. How this happens can be shown in two dimensions.
A few examples would convince us that it is extremely easy to change a formula entirely by the mere change of mesh systems. It seems unnecessary to emphasize the fact that 'universal laws', to be 'universal', should not depend structurally to such an extent on the accidental and, after all, unimportant, choice of reference systems.^{8}
To remedy such a state of affairs, impossible in mature science, the tensor calculus was invented. The whole general theory of Einstein seems to demand that the equations of physics should ultimately be expressed in tensor forms; in other words, that 'universal laws' should cease to be 'local gossip'; a demand which must be granted, and on this point the Einstein theory is beyond criticism and is an epochal methodological advance of an irreversible structural linguistic character.
Section C. Spacetime. 




In dealing with coordinate systems we have heretofore used them to represent only 'spatial' entities, spreads of different dimensions. It is desirable to become acquainted with a different use of coordinates, in which one of them will represent 'time'. The last use is just as simple as the former, but the graphs which we obtain are different.

