Geomagnetic data from the astronomical observatory of Madrid (1879-1901)

The recovery of early geomagnetic data is essential to improve knowledge of the evolution of the geomagnetic field. A recently recovered dataset is described that includes mean decadal (ten day) values of the geomagnetic declination and some disperse values of geomagnetic inclination measured at the Astronomical Observatory of Madrid from 1879 to 1901. These recovered data are compared directly with the results obtained from a geomagnetic model. The data have now been made accessible for the scientific community in digital form.