IF electrostatic measurements are made in the air on a bridge over the permanent way near any railway station, extraordinarily large positive charges given off by steam locomotives will be observed, especially on starting up. These positive charges are carried by the wind for long distances. Under favourable conditions, that is, when the sky was clear and free from interference from clouds, and a stiff steady wind prevailed, I have noticed strong charges down wind a mile away, from a single engine working in a country siding. Scarcely any effect is noticeable in the opposite direction. Similar results, although on a much smaller scale, are observed near steam-driven road engines. They are not noticeable near petrol-driven or electric traction. These charges are presumably similar to those employed in Sir W. Armstrong's hydroelectric machine.