Non-Euclidean geometry; a critical and historical study of its development. Authorized English translation with additional appendices Q Science
Achatinellen-Fauna der Sandwich-Insel Molokai nebst einem Verzeichnis der übrigen daselbst vorkommenden Land- u. Süsswassermollusken Q Science
The philosophy of arithmetic as developed from the three fundamental processes of synthesis, analysis and comparison, containing also a history of arithmetic Q Science
