This device, as shown in the accompanying illustration, is a glass cylinder fixed on an ebonite base, and closed at the top by an ebonite cap. A solid brass rod runs from top to bottom, and near the bottom, and at right angles to it, is fixed a smaller adjustable rod, terminating in a flat head. Opposite to this flat disk there is a brass strip secured to the ebonite cap. From the top of this brass strip hangs a gold or aluminum foil. The foil and strip are placed to earth, and the solid brass rod is connected to the circuit to be protected. Should the difference of potential between the foil and the terminal opposite to it attain more than a certain amount, electrostatic attraction will cause the foil to touch the disk and place the circuit to earth. The apparatus, which is a modification of the Cardew earthing device, is constructed by Messrs. Drake & Gorham, of Victoria Street.--_The Electrician_. [Illustration.] * * * * * EXPERIMENTS WITH HIGH TENSION ALTERNATING CURRENTS. Messrs. Siemens and Halske, of Berlin, recently invited the members of the Elektrotechnische Verein of that city to their works to witness the demonstration of a series of experiments on alternating currents under a pressure of 20,000 volts. In order to show that the desired pressure was really _en evidence_, the high tension was conducted through a pair of wires of only 0.2 mm. diameter to a battery of 200 100-volt incandescent lamps, all connected up in series. An ordinary Siemens electric light cable was inserted, and broke down at a pressure of some 15,000 volts. At the end of the meeting a few experiments on the formation of the arc under this enormous pressure were shown. The sparking distance varied considerably, according to the shape of the electrodes. At 20,000 volts a spark jumped from a ball to a ball about 10 millimeters, while between two points a sparking distance of 30 millimeters, and sometimes even more, was reached. This arc is shown half size in the accompanying engraving. [Illustration: A 20,000 VOLT ALTERNATING ARC (half size).] The arc which followed the jumping over of a spark made a loud humming and clapping noise, and flapped about, being easily carried away by the slightest draught. The arc could be drawn out horizontally to something like 100 millimeters distance between the electrodes, and even to a distance of 150 millimeters, when carbon pencils were used as electrodes, but it always remained standing up in a point. --_Electrical Engineer._ * * * * * THE RELATION OF BACTERIA TO PRACTICAL SURGERY.[1] [Footnote 1: The address in surgery delivered before the Medical Society of the State of Pennsylvania, June 4, 1890.] By JOHN B. ROBERTS, A.M., M.D., Professor of Surgery in the Woman's Medical College and in the Philadelphia Polyclinic.