D O C U M E N T 3 6 3 A U G U S T 1 9 2 6 3 5 9 ordinate space are very hard to digest, also the lack of any understanding of the fre- quency of emitted light.— I already wrote to you about this, that the canal ray experiments came out entirely in line with the wave theory.[8] Here waves, here quanta! The reality of both is rock solid. Only the devil can make any real rhyme or reason out of it. Warm regards to all of you from your Albert Best regards also to the De Haases.[9] I know a particularly good diagnostician over here. It might not be silly if De Haas came here once to be looked at, in case the cause of his ailment is unclear.[10] 363. From Oskar Klein Gilleleje, 29 August 1926 Dear Professor, I heard yesterday from Prof. Ehrenfest[1] that you would like to see what I wrote about quantum theory and five-dimensional relativity theory. This pleases me very much and I send you herewith an offprint[2] and a copy of a few pages that I am perhaps going to send to Nature.[3] In a few days I would also like to send you a short unpublished note, of which I don’t have a copy at the moment. You will see from these writings that I am very much a pupil of yours. I hope to have an opportunity once to hear your opinion on these questions. As concerns the further extension of this, it seems to me that the assumption of a periodicity in is essential.[4] I am now thinking of attempting, in the general equations, ( will be the tensor corresponding to )[5] , to average over the fifth coordinate and, at the same time, to assume that the deriv- atives of the ’s are relatively very large.[6] I have some hope that the matter ten- sor will appear herewith as the one part of the s dependent on and on ,[7] and that perhaps will appear as a Schrödinger function.[8] But all of this is hardly sketched out yet. Respectfully yours, Oskar Klein If Prof. Bohr[9] knew that I was writing to you, he would surely send his most cordial greetings. He is on vacation at the moment, but is probably already coming back to Copenhagen tomorrow. x0 Pik 0= Pik Rik i k , 0 1 12 3 4) , , , , = ( x0 Pik γ00 x0 γ00