This was a preliminary notice of the results of a series of experiments devised to test the part played by water-vapour in the production of atmospheric electricity. While water is in the form of vapour it must be electrified by contact with the gases of the atmosphere—as they are by contact with one another. Precipitation of vapour in a receiver, whether produced by cold or by exhaustion, was found to be steadily accompanied with a disengagement of electricity. Further experiments are to be made with receivers of very great capacity.