Jama near Predjama and Postojnska Jama, Slovenia, are known for their rich body of historic inscriptions spanning over several centuries. Early explorers and visitors left names, dates and symbols. Here we present the inscriptions by the mathematician Josef Anton Nagel (1717-1794). Nagel and the painter and engineer Alois Schaffenrath (1794-1836) are the only ones that we can trace in both of the caves. Nagel visited the caves in July 1748 on order of Emperor Franz I. The inscription in Jama near Predjama is (for cave inscriptions) rather long and written in Latin, giving name, profession, cause and date of the visit, while the inscription in Postojnska Jama is rather short, giving only name and date of visit. Unfortunately the inscription in Jama near Predjama is already partly obliterated by an incautious visitor.