[Illustration.]

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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.

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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.

The revolution which has occurred in practical surgery since the discovery of the relation of micro-organisms to the complications occurring in wounds has caused me to select this subject for discussion.  Although many of my hearers are familiar with the germ theory of disease, it is possible that it may interest some of them to have put before them in a short address a few points in bacteriology which are of value to the practical surgeon.

It must be remembered that the groups of symptoms which were formerly classed under the heads “inflammatory fever,” “symptomatic fever,” “traumatic fever,” “hectic fever,” and similar terms, varying in name with the surgeon speaking of them, or with the location of the disease, are now known to be due to the invasion of the wound by microscopic plants.  These bacteria, after entering the blood