Dangerous Electricity

Conditions Under Which Contact with the Fatal Current Is Rendered Harmless.

A great sensation was produced 10 or 12 years ago, when a prominent American electrician, Nikola Tesla, exposed himself to the effects of a current whose pressure was said to be a million volts. Well, there may have been some exaggeration in that statement, observes the New York Tribune, but there seems to be no question that the voltage was far beyond what was then regarded the limit of safety. A trolley current has a pressure of between 500 and 600 volts, and, while it cannot well prove fatal, it is a thing to be treated respectfully. For the execution of the death penalty, at Sing Sing and Auburn prisons, it is customary to employ only about 1,500 or 1,800 volts.

Now, there were two things about Tesla’s experiment which, in combination, afforded comparative immunity. One was that he did not use the continuous, or direct, current, but an alternating current. That is to say, the electricity first flowed in one direction and then in the opposite, the changes occurring with extraordinary frequency. If they had been produced at the rate of only one or two or 25 or 30 per second, serious harm would have resulted. The alternations which Tesla caused numbered many thousands — perhaps a million a second. What he showed, therefore, was that if the frequency were high enough, almost any voltage could be handled with impunity. The feat was spectacular, but of little practical value, because for such things as lighting a low frequency is preferable. Nevertheless, the revelation set scientific men to speculating over the cause of Mr. Tesla’s immunity. A favorite theory at that time was that the action of the current was confined to the skin, and did not get below the latter.

Prof. Nernst, inventor of an electric lamp that has proved more popular in Europe than America, now questions that conclusion. In a communication to the Bunsen society, he expresses the opinion that high frequency currents do penetrate the soft cellular tissues beneath the skin, but that they do not have time to work any change in it because the reversal of direction comes so rapid. Of course the correctness of either explanation is of less importance than the main fact, but the human mind is so constituted that it always wants to know the reason for strange things. As yet other scientists have not publicly pronounced upon the accuracy of Prof. Nernst’s views, but will doubtless do so in time.

With direct and low frequency alternating currents accidents sometimes happen which are not followed by the consequences which might naturally be expected. One often reads an account of what seems to be, and probably is, a narrow escape. A person is exposed to a current of high voltage and receives a painful shock, but is practically unhurt. For such incidents there are a variety of explanations. If a bare wire is touched with perfectly dry hands or with greasy hands, the effect is trifling. A good electrical contact between metal and flesh is obtained only when the latter is moist. Grease acts as an insulator. Dry clothing does, too. Moreover, there is no likelihood that electricity will bother a person unless he makes two good contacts, and the current can flow through him. It must be able to get out as well as to get in. A man might bend over and touch a third rail, used to operate an electric railway, but he would not feel any effect unless some other part of his body simultaneously rested on a second metallic object, which formed part of the circuit. One contact is not enough.