we shall find a greater acceleration than 981 for the body itself.

Thus we see that we, also when the measure is not attached to the
earth, disregarding its displacement, may describe the motion of the
body in respect to the measure always in the same way--i.e., as one
uniformly accelerated, as we ascribe now and again a fixed value to
the acceleration of the sphere of gravitation, in a particular case
the value of zero.

Of course, in the case here under consideration the use of a measure
fixed immovably upon the earth should merit all recommendation. But
in the spaces of the solar system we have, now that we have abandoned
the ether, no such support. We can no longer establish a system of
co-ordinates, like the one just mentioned, in a universal intermediate
matter, and if we were to arrive in one way or another at a definite
system of lines crossing each other in three directions, then we should
be able to use just as well another similar system that in respect to
the first moves this or that way. We should also be able to remodel the
system of co-ordinates in all kinds of ways, for example by extension
or compression. That in all these cases for fixed bodies that do not
participate in the movement or the remodelling of the system other
co-ordinates will be read off again and again is clear.



NEW SYSTEM OR CO-ORDINATES

What way Einstein had to follow is now apparent. He must--this
hardly needs to be said--in calculating definite, particular cases
make use of a chosen system of co-ordinates, but as he had no means