Last time I provided a list of works on the philosophy of mathematics in the School of Brentano and claimed that most of them were in the public domain and available on-line. However, the material isn’t exactly easy to find. So here’s the list again, now with bibliographical references and links where possible:

• Carl Stumpf’s 1870 habilitation essay Über die Grundsätze der Mathematik (On the Foundations of Mathematics), was only recently published, edited by Wolfgang Ewen with Königshausen & Neumann (2008).
• Benno Kerry’s habilitation thesis Grundzüge einer Theorie der mathematischen und nicht-mathematischen Grenzbegriffe (Fundamental Outline of a Theory of Mathematical and non-Mathematical limit Concepts) in 1885, published posthumously in 1890 as System einer Theorie der Grenzbegriffe. Ein Beitrag zur Erkenntnistheorie I, Leipzig, Deuticke, available from Archive.org (with an atrocious typo in the title).
• Christian von Ehrenfels’ 1885 dissertation Größenrelationen und Zahlen: Eine psychologische Studie (Relations of Magnitude and Numbers. A psychological Study), unpublished, not online, manuscript and typoscript conserved at the Forschungsstelle und Dokumentationszentrum für Österreichische Philosophie in Graz.
• Edmund Husserl’s habilitation work Über den Begriff der Zahl (On the Concept of Number) in 1887, like all of Husserl’s works published during his lifetime, available from the university of Freiburg.
• Konrad Zindler’s 1889 prize-winning essay “Beiträge zur Theorie der Mathematischen Erkenntniss” (“Contributions to the Theory of Mathematical Knowledge”), published in the Sitzungsberichte der Kais. Akademie der Wissenschaften in Wien philos-histor. Klasse. Bd. 118, IX Abhandlung, pp. 1-98, which is available in its entirety from Archive.org.
• Ehrenfels’ article “Zur Philosophie der Mathematik” (“On the Philosophy of Mathematics”) in 1891 in the Vierteljahrsschrift für wissenschaftliche Philosophie 15, pp. 285–347. The Vierteljahrsschrift is available at the French National Library.
• Husserl’s Philosophie der Arithmetik (Philosophy of Arithmetic) of 1891, available from the university of Freiburg.
• Stumpf’s Über den Begriff der mathematischen Wahrscheinlichkeit in 1892, published in the Sitzungsberichte der philosophisch -philologischen und der historischen Classe der k. b. Akademie der Wissenschaften zu München, 1893, pp. 37-120, the whole journal issue is available on Archive.org.

Kerry’s series of articles “Über Anschauung und ihre psychische Verarbeitung” were published in the Vierteljahrsschrift: 9, 1885, p.433-493; 10, 1886, p. 419-467; 11, 1887, p. 53-116; p. 249-307; 13, 1889, p. 71-124; p. 392-419; 14, 1890, p. 317-353; and 15, 1891, p. 127-167, all available from the French National Library.

Höfler and Meinong’s 1890 Logik is likewise available from Archive.org (again with a mangled title).