APPENDIX: A SELECTION OF DOCUMENTS1 1) A letter from Felix Klein to Heinrich von Mühler, the Prussian Minister of Religious, Educational, and Medical Affairs (Minister of Culture).2 Your Excellency, Düsseldorf – December 19, 1870 In a request dated March 7th of this year, I took the liberty of asking for diplomatic recommendations to travel to France and England for the purpose of undertaking a scientific trip. At the same time, I had offered to submit reports on the conditions of mathematics in these countries upon my return. On March 26th, I was fortunate enough to receive a reply from your Excellency (U 7737) to the effect that the diplomatic recommendations in question had been granted to me, and that your Excellency would be pleased to receive reports on the present state of French and English mathematics. Under the prevailing conditions, unfortunately, the trip could not be underta- ken in the way that I intended. My stay in Paris, where I had arrived on April 19th, was suddenly interrupted by the declaration of war on July 16th. I rushed home (Düsseldorf) and, because I was deemed unfit for military service at the moment by the relevant authorities, I joined an association for voluntary medical care, which had meanwhile been established in Bonn. As a member of this association, I spent the period from August 16th to October 2nd, when I was discharged to re- turn home on account of my poor health, in the theater of war. Having only recently recovered, I did not want to make the trip to England because of the time that I had lost. Rather, I have already applied to habilitate in Göttingen and become a Privatdozent of mathematics there, and I intend to move there at the New Year. Given that it is not possible for me to send you reports on French and English mathematics in the way that I intended, I would at least like to enclose a copy of a short report on French mathematics, which I composed together with one of my student friends (Dr. Lie from Christiania), to demonstrate that I had worked along these lines during my stay in Paris. We had prepared this report for the mathema- tical [student] union at the University of Berlin and had sent it to this organization on July 7th. At the same time, allow me to enclose an article, “Sur une certaine famille de courbes et de surfaces,” which my friend Lie and I coauthored. We presented this work to the Académie des Sciences in two sessions, on the 6th and 13th of June, and the Académie published it in its Comptes Rendus. By choosing this publica- 1 The original German documents are published in TOBIES 2019, pp. 495–524. 2 [Stabi] Sammlung Darmstaedter. See also Section 2.6.3. © Springer Nature Switzerland AG 2021 593 R. Tobies, Felix Klein, Vita Mathematica 20, https://doi.org/10.1007/978-3-030-75785-4 594 Appendix: A Selection of Documents tion venue, we hoped to gain deeper insight into the conditions there and to be- come personally acquainted with a large number of French mathematicians, and we succeeded in doing so. Finally, allow me to add that we obtained further results – “Ueber die Haupt- tangenten-Curven der Kummer’schen Fläche vierten Grades mit 16 Knotenpunk- ten” [On the Main Tangent Curves of the Fourth-Degree Kummer Surface with 16 Nodal Points] – and we recently informed Professor Kummer privately about them. At his request, we submitted this work to the Academy of Sciences in Ber- lin, which will publish it in its monthly reports with the date of December 15th. By expressing my deepest thanks to your Excellency for your friendly appro- val of my initial request and by asking for more of your kindness in the future, I remain your Excellency’s most respectfully devoted Dr. Felix Klein. 2) An application submitted by Felix Klein to the Academic Senate of the Univer- sity of Erlangen for funding to improve the collection of the University Library’s mathematical section (November 15, 1872).3 Royal Academic Senate! For the purposes of a mathematician, a small library may be sufficient, but it must be entirely at his disposal, for he must constantly refer to it in the interests of his research and teaching. The mathematical section of the University Library here, however, is unfortunately not in a state that meets even the most modest re- quirements. Allow me to begin by briefly explaining its main lacunae to the Royal Senate. The so-called mathematical section of the University Library consists of ap- proximately 1,200 volumes. A great majority of these, however, is utterly worthless for today’s university purposes because they pertain to engineering, architecture, etc. The smaller minority of genuinely mathematical and related works was not collected according to a uniform principle; rather, chance has played an ever-shifting role in these acquisitions, so that, besides the several works that are worthy of attention, there are also almost unbelievable gaps. Of the works by older authors, for example, the writings of Galileo and New- ton are available almost in their entirety, but the library has only the last three volumes of the new complete edition of Kepler’s works, and it lacks the most im- portant items in its collection of works by Huygens, Euler, and Lagrange. Regarding the collection of mathematical journals, the German ones (to the extent that they should be considered) are all available, but the foreign journals are entirely lacking. This is all the more regrettable because mathematics is a tho- roughly international science, and the progress of a productive mathematician is considerably hindered without him having a universal overview of the findings of others at the same time. In light of the burden that the ongoing acquisition of an 3 [UA Erlangen] Ph. Th. I Pos. 20 V, No. 8. On the context of this application, see Section 3.3. Appendix: A Selection of Documents 595 additional journal represents for the library’s budget, however, I believe that I should limit my requests. My only proposal is that it should subscribe to a French journal which contains up-to-date reports on recent publications: the Bulletin des sciences mathématiques et astronomiques, edited by Darboux. Some time ago, a number of astronomical journals had also been acquired. With the sole exception of the Annalen published by the observatory in Munich, all of them break off at different times without any apparent reason. For example, complete holdings of the Berliner [Astronomisches] Jahrbuch exist from its be- ginning in 1776 to 1861. I suggest that the missing volumes should be purchased and that the subscription to this Jahrbuch should be renewed. As far as recent books are concerned, geometry is relatively the best-repre- sented of the mathematical disciplines, given that a preference for geometry has always been cultivated in Erlangen. Yet it is far from the level of completeness that I would hope for it to achieve over time; in particular, the collection lacks certain handbooks that seem to be suited for providing an introduction to the spe- cial study of geometry. Other branches of mathematics are in part almost entirely unrepresented, and these are hardly unimportant. On mechanics, for example, there is nothing aside from Poisson’s excellent book; likewise, the most important new works on diffe- rential and integral calculus are also lacking; there is nothing to be found on ma- thematical physics, unless there happens to be something useful in the physics section. In these disciplines, it is necessary to create adequate conditions by filling in the discernible gaps, so that the most necessary items are available – failing which constructive instruction is not conceivable at all. I therefore take the liberty of requesting the Royal Academic Senate to apply to the highest authority [the Bavarian Ministry of Culture] for a sum of 350 Gul- den to be allotted from the University’s surplus funds for the purpose of comple- ting the mathematical section of the University Library on the basis of an enclosed cost estimate, the individual items of which are justified in the explanations above. Respectfully and with devotion to the Royal Academic Senate, Felix Klein Professor of Mathematics4 4 Dean Eugen Lommel, a professor of physics known today for the Lommel function and the Lommel differential equation, forwarded Klein’s application with an expert opinion to the Bavarian Ministry of Culture, which granted his request for 350 Gulden ([UA Erlangen] Ph. Th, I. Pos. 20 V. No. 8). – Klein’s abbreviated book titles list (see below) is translated into English; “G” designates a book by a German author or a translation into German; for exam- ple: L. Cremona, Einleitung in eine geometrische Theorie der ebenen Curven (Greifswald: Koch, 1865); Poinsot’s Elemente der Statik, als Lehrbuch für den öffentlichen Unterricht und zum Selbststudium (Berlin: Rücker, 1835); Duhamel, Lehrbuch der reinen Mechanik (Braun- schweig: Vieweg, 1853). 596 Appendix: A Selection of Documents Cost Estimate for Completing the Mathematical Section of the University Library Older Works Kepler’s Collected Works. Vols.1–5 ................................... 25.- Euler. Introductio in analysin ............................................ 5.- Calculus differentialis ............................................. 7.20 Mechanica ............................................................... 6.- Methodus inveniendi lineas curvas ......................... 4.- Lagrange. Mécanique analytique ........................................... 15.- Huygens. Horologium oscillatorium ....................................... 3.- Updating the Journal Collection. Darboux. Bulletin. Two volumes ........................................... 11.- Astronomical Yearbook. Ten volumes G .............. 20.- Geometry. Grassmann. Extension Theory 1, 2 G ........................................... 3.15 Plücker. Analyt. geometr. Developments G ........................... 1.10 Algebraic Curves G .................................................. 1.25 Hesse. Lectures. Space, Planes G ......................................... 4.20 Salmon. Geometry of Planes, of Space G .............................. 9.14 Reye. Geometry of Position G ........................................... 3.- Cremona. Plane Curves G .......................................................