Spain was a scientifically backward country in the early 19th-century. Thecauses were various political events, the War of Independence, and the reign ofFernando VII. The introduction of contemporary physics into textbooks wastherefore a slow process. An analysis of the contents of 19th-century Spanishtextbooks is here presented, centred on imponderable fluids, the concept ofenergy, the mechanical theory of heat, and the kinetic theory of gases.