Hantzel has communicated to the Saxon Royal Society of Science some interesting observations on the production of electricity by light in colored fluor-spar. The centers of the fluor-spar cubes become negatively electric by the action of light. The electric tension diminishes toward the edges and angles, and frequently positive polarity is produced there. With very sensitive crystals a short exposure to daylight is sufficient; by a long exposure to light the electric current increases. The direct rays of the sun act much more powerfully than diffused daylight, and the electric carbon light is more powerful even than sunlight. The photo-electric action of light belongs principally to the "chemically active" rays; this is shown by the fact that the production of electricity is extremely small behind a glass colored with cuprous oxide, and behind a film of a solution of quinine sulphate; while it is not appreciably diminished by a film of a solution of alum. The photo-electric excitability of fluor-spar crystals is increased by a moderate heat (80° to 100° C.). * * * * * THE AURORA BOREALIS AND TELEGRAPH CABLES. The January and February numbers of the _Elektrotechnische Zeitschrift_ contain a number of articles on this interesting subject by several eminent electricians. Professor Foerster, director of the observatory in Berlin, points out the great importance of the careful study of earth currents, first observed at Greenwich, and now being investigated by a committee appointed by the German Government. He further points out, according to Professor Wykander, of Lund, in Sweden, that a close connection exists between earth currents, the protuberances of the sun, and the aurora borealis, and that the nearly regular periodical reappearance of protuberances in intervals of eleven years coincides with similar periods of excessive magnetic earth currents and the appearance of the aurora borealis. The remarkable disturbing influences on telegraph wires and cables of the aurora borealis observed from the 11th to 14th of August, 1880, have been carefully recorded by Herr Geh. Postnath Ludwig in Berlin, and a map of Europe compiled, showing the places affected, with the extent to which telegraph wires and cables were influenced and disturbed. Although the aurora was but faintly visible in England and Germany, and in Russia only as far as 35° north, disturbing influences were reported from all parts of Europe, the Mediterranean, and Africa, and even Japan and the east coast of Asia. As far south as Zanzibar, Mozambique, and Natal disturbances were also noticed. They were in Europe most intense on the morning of August 12, when they lasted the whole day, and increased again in intensity toward eight o'clock in the evening, while they suddenly ceased everywhere almost simultaneously. Scientific and careful observations were only taken at a few places, but the existence of earth currents in frequently