are so small compared to 1 that we can neglect the higher powers of the
and their derivatives. If we do this, we learn nothing about the structure of the gravitational held, or of metrical space of cosmical dimensions, but we do learn about the influence of neighbouring masses upon physical phenomena.
Before carrying through this approximation we shall transform (96). We multiply (96) by
, summed over the
and
observing the relation which follows from the definition of the