5 2 D O C U M E N T S 5 9 , 6 0 F E B R U A R Y 1 9 2 1
know how far the above scalar (of second order in the second derivatives of the
’s) is the only one having the required property. I am convinced that you have
thus done relativity theory an inestimable service. For it is now a simple matter to
construct a theory of relativity that assigns meaning to the ratios of the ’s, or
the equation , without—as with Weyl—, in my conviction, the
physically meaningless quantities (electromagnetic potentials) explicitly
appearing in the equations. There only remains the problem of whether Nature
really has made use of this possibility available to her to constrain herself accord-
ingly. As soon as I have formed a judgment about this, I shall give myself the plea-
sure of informing you of the details.
With cordial thanks once again and kind regards, I am yours very sincerely,
sig. A. Einstein.
59. From Otto Neurath
Vienna, 22 February 1921
As you know, the matter is being discussed provisionally with Frank and Dr.
Löwy. Further negotiations will be considered only upon your consent. I ask
you please to choose the alternative to have the previously agreed upon in the
required exhaustive letter forwarded to me and to add at the end the sentence: “I
must, of course, reserve the right to withhold my binding consent until the agree-
ments with the publisher and other editors exist.” Thus you are not bound in any
way and I can continue the negotiations anyway.
In hope of a prompt reply, very respectfully,
60. To Carl Beck
Berlin, 23 February 1921
Highly esteemed Professor Beck,
It was a great kindness of you to write to me in such detail and offer your valu-
able assistance. During the course of the past half year I have been receiving invi-
tations from a number of American universities. Nevertheless I gave up
undertaking a lecture tour to America for various reasons. Now suddenly the neces-
g dx dx 0 =