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We start off on a consideration of a Galileian domain, i.e. a

domain in which there is no gravitational field relative to the

Galileian reference-body K. The behaviour of measuring-rods and

clocks with reference to K is known from the special theory of

relativity, likewise the behaviour of "isolated" material points;

the latter move uniformly and in straight lines.

Now let us refer this domain to a random Gauss coordinate system

or to a "mollusc" as reference-body K′. Then with respect to K′

there is a gravitational field G (of a particular kind). We learn

the behaviour of measuring-rods and clocks and also of

freely-moving material points with reference to K′ simply by

mathematical transformation. We interpret this behaviour as the

behaviour of measuring-rods, clocks and material points under the

influence of the gravitational field G. Hereupon we introduce a

hypothesis: that the influence of the gravitational field on

measuring-rods, clocks and freely-moving material points

continues to take place according to the same laws, even in the

case where the prevailing gravitational field is not derivable

from the Galileian special case, simply by means of a

transformation of co-ordinates.