Goor, J. van. “W. Otterspeer, Leiden Oriental Connections 1850-1940”. BMGN - Low Countries Historical Review 110, no. 1 (January 1, 1995): 137–140. Accessed April 26, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-104582.