The interplanetary magnetic field (IMF) By component affects the configuration of field-aligned currents (FAC) whose geomagnetic response is observed from high to low latitudes. The ground magnetic perturbations induced by FACs are opposite on the dawn and dusk sides and depend upon the IMF By polarity. Based on the multilinear regression analysis, we show that this effect is presented at the mid-latitude observatories, Niemegk and Arti, in the X and Y components of the geomagnetic field. This allows us to infer the IMF sector structure from the old geomagnetic records made at Ekaterinburg and Potsdam since 1850 and 1890, respectively. Geomagnetic data from various stations provide proxies of the IMF polarity which coincide for the most part of the 19th and 20th centuries. This supports their reliabilities and makes them suitable for studying the large-scale IMF sector structure in the past.