N. J. (Nels Johann) Lennes

Born in 1874, N. J. Lennes was a mathematician and educator best known for writing clear, classroom-focused books on geometry, algebra, and arithmetic.

His work appears in major public-domain collections today, including Project Gutenberg, where many of his textbooks have been preserved. The surviving record available here points to him primarily as a teacher and author whose books were designed to help students build solid mathematical habits through practice and application.

I couldn’t confirm enough reliable biographical detail in the sources I found to go much further than that, so this overview keeps to the basics.