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A priori it is by no means certain that this last measurement

will supply us with the same result as the first. Thus the length

of the train as measured from the embankment may be different

from that obtained by measuring in the train itself. This

circumstance leads us to a second objection which must be raised

against the apparently obvious consideration of Section VI.

Namely, if the man in the carriage covers the distance w in a

unit of time-_measured from the train,-then this distance-as

measured from the embankment_ is not necessarily also equal to w.

XI.

THE LORENTZ TRANSFORMATION

The results of the last three sections show that the apparent

incompatibility of the law of propagation of light with the

principle of relativity (Section VII) has been derived by means

of a consideration which borrowed two unjustifiable hypotheses

from classical mechanics; these are as follows: