'SUBTLE is THE LORD' 125
Like Voigt before him, Lorentz regarded the transformations (Eqs. 6.9 and
6.10) only as a convenient mathematical tool for proving a physical theorem, in
his case that to O(v/c) terrestrial optical experiments are independent of the
motion of the earth, a result already mentioned in Section 6a. Equation 6.9 was
obviously familiar to Lorentz, but the novel Eq. 6.10 led him to introduce signif-
icant new terminology. He proposed to call t the general time and t' the local time
[L16]. Although he did not say so explicitly, it is evident that to him there was,
so to speak, only one true time: t. At this stage, Lorentz's explanation for the
absence of any evidence for a stationary aether was hybrid in character: to first
order he had derived the null effects from electrodynamics; to second order he had
to introduce his ad hoc hypothesis expressed by Eq. 6.8.
One last remark on the 1895 paper. It contains another novelty, the assumption
that an 'ion' with charge e and velocity v is subject to a force K:
the Lorentz force (Lorentz called it the electrische Kraft [L17]).
As has been noted repeatedly, in 1905 Einstein knew of Lorentz's work only
up to 1895. Thus Einstein was aware of no more and no less than the following:
Lorentz's concern about the Michelson-Morley experiment, his 'first-order
Lorentz transformation,' Eqs. 6.9 and 6.10, his proof of the first-order theorem
for optical phenomena, his need to supplement this proof with the contraction
hypothesis, and, finally, his new postulate of the Lorentz force, Eq. 6.13.
As a conclusion to the contributions of Lorentz prior to 1905, the following
three papers need to be mentioned.
- Lorentz discusses the status of his work in a lecture given in Diisseldorf
[LI8]. It is essentially a summary of what he had written in 1895. - He gives a 'simplified version' of his earlier theory [L19]. Five years
later, he characterized this work as follows. 'It would be more satisfactory if it
were possible to show, by means of certain fundamental assumptions, and without
neglecting terms of one order of magnitude or another, that many electromagnetic
actions are entirely independent of the motion of the system. Some years ago [in
1899] I had already sought to frame a theory of this kind' [L20]. In 1899 he wrote
down the transformations
which are the Lorentz transformations (Eq. 6.3) up to a scale factor €. He noted
among other things that 'the dilatations determined by [Eqs. 6.14 and 6.15] are
precisely those which I had to assume in order to explain the experiment of Mr
Michelson'! Thus the reduction of the FitzGerald-Lorentz contraction to a con-