D O C . 1 5 3 O C T O B E R 1 9 1 9 1 3 1
When I had a look at these publications, I found in yours a downright comical
concurrence with my already finished script and thought better of submitting it to
the press. When I looked through Harzer’s calculations, my opinion changed again.
For I have some reservations about Harzer. First, his mathematical starting assump-
tions are anything but clear in relativity theory. I was able to prove them at last,
though, but doubt whether very many other colleagues in the field would be able to
repeat my proof. Whether Fresnel’s hypothesis, from which Harzer derives his laws
of reflection and refraction of moving surfaces, agrees with the theory of relativity
does seem quite questionable to me, however. Otherwise, and this is probably most
important, I can frame the theory much more simply and incontrovertibly, whereby
I conclude from the theorem of a preferred light path (Fermat’s principle) that the
displacement of the light path contributes nothing of first order in q/c to the time
that the light needs between a point P and a point Q of the interferometer’s separa-
tion plane. For then I can calculate as though all the rays were straight and as
though the law of reflection were as for surfaces at rest.
Harzer himself noticed that the displacement of the ray path is as good as insig-
nificant to the final result. He is extremely astonished by that; and if he saw this not
from his formula but only from the calculations, then that is based on another mis-
take of his. For he completely forgets that the air distances within the interferom-
eter also contribute a little to the fringe displacement. All in all, there is so much to
criticize in this calculation; moreover, it is written so indigestibly and is so inacces-
sible to physicists that I am going to submit my paper to the Annalen now after
It goes without saying that all the requisite citations will appear in it.
That is why the question I posed to you in the last letter remains important to me.
I would be very grateful to you for a not too tardy
With cordial regards, yours,
153. From Hendrik A. Lorentz
Haarlem, 30 October 1919
I forgot to ask you to give Planck my cordial regards, when you see
Also, I neglected to tell you that Coster really was right with his comment during
In the problem of the drag of a small sphere that is suspended in a
fluid set in motion by friction, one ultimately arrives at an expression that contains