D O C . 2 6 A P R I L 1 9 1 9 2 1 To resolve this question, we intend to analyze more closely the structure of the selected lines by using a microphotometer, but are not in possession of a suitable instrument. Toward procurement of a microphotometer from P. P. Koch, we therefore peti- tion funding from the Kaiser Wilhelm Institute of Physics, which we estimate at about 2000 marks, and ask you to kindly give your support for approval by the re- sponsible authority. In great respect, faithfully, Prof. Dr. L. Grebe. 1. To Theodor Kaluza [Berlin,] 21 April 1919 Dear Colleague,[1] The thought that electric fields are truncated ’s has often preoccupied me as well. But the idea of achieving this with a five-dimensional cylindrical world never occurred to me and may well be altogether new.[2] At first glance your idea has great appeal for me. It seems to me to have decidedly more promise from the physical point of view than the mathematically probing exploration by Weyl, be- cause it starts with the electric field and not with the physically meaningless—I am convinced—four potential.[3] Moreover, your theory leaves the four-dimensional[4]too.nicevery geodesic line (trace of the chargeless mass-point) intact, which is very nice too.[4]I It now all depends on whether your idea will withstand physical scrutiny. I would like to mention two points: 1. It must be reconcilable with the existence of different positive and negative elementary quanta. With your Ansatz[5] (to what kind of a line does the derivative refer?), this not seem to be the case, because it only seems to permit the positive sign of . But you will surely consider this more thoroughly. 2. The cosmological problem must be resolvable in a reasonable way. Provided that upon reading your more thorough exposition I do not see what I would consider to be some crushing objection that cannot be resolved, I am gladlythe prepared to present a paper by you on the subject before the local Academy (for the proceedings). The advantage would be that you would not have to wait for μν ρ ⎩ ⎭ ⎨ ⎬ ⎧ ⎫ ρ0 ε--------- ds = dw0 ds --------- ρ0 To resolve this question, we intend to analyze more closely the structure of the selected lines by using a microphotometer, but are not in possession of a suitable instrument. Toward procurement of a microphotometer from P. P. Koch, we therefore peti- tion funding from the Kaiser Wilhelm Institute of Physics, which we estimate at about 2000 marks, and ask you to kindly give your support for approval by the re- sponsible authority. With great respect, faithfully, Prof. Dr. L. Grebe. 26. To Theodor Kaluza [Berlin,] 21 April 1919 Dear Colleague,[1] The thought that electric fields are truncated ’s has often preoccupied me as well. But the idea of achieving this with a five-dimensional cylindrical world never occurred to me and may well be altogether new.[2] At first glance your idea has great appeal for me. It seems to me to have decidedly more promise from the physical point of view than the mathematically probing exploration by Weyl, be- cause it starts with the electric field and not with the physically meaningless—I am convinced—four potential .[3] Moreover, your theory leaves the four-dimensional geodesic line (trace of the chargeless mass-point) intact, which is It now all depends on whether your idea will withstand physical scrutiny. would like to mention two points: 1. It must be reconcilable with the existence of different positive and negative elementary quanta. With your Ansatz [5] (to what kind of a line does the derivative refer?), this does not seem to be the case, because it only seems to permit the positive sign of . But you will surely consider this more thoroughly. 2. The cosmological problem must be resolvable in a reasonable way. Provided that upon reading your more thorough exposition I do not see what I would consider to be some crushing objection that cannot be resolved, I am gladly prepared to present a paper by you on the subject before the local Academy (for proceedings). The advantage would be that you would not have to wait for publication. [6] However, you would then have to make sure that the paper does not μν ρ ⎩ ⎭ ⎨ ⎬ ⎧ ⎫ ρ0 εdw0 dw0 ds --------- = dw0 ds --------- ρdoes 0