A story is told of an Eastern prince who bought a slave who proved to be a magician. The slave at first fascinated his master with his countless tricks and wonders; but after a while the master became terrified at the evil resources of his slave, and besought him to leave him, giving him his freedom. Electricity is the slave of man; but at times it bids fair to overcome the master.
Our horses may be said to reflect public sentiment in regard to one of the common applications of electricity, — that of the propulsion of electric cars. At first they were afraid. Their nervous trepidation in some cases broke down all the barriers of restraint. Now they are becoming used to the car which moves so mysteriously. The inevitable has come; and it is perhaps horse sense to acquiesce.
It is true that there are dangers lurking in the electric-car system; but it is probable that the inside of the electric car is a safer place than the outside. By no possibility can the electric motor explode. The chances of any one getting a deadly shock from the current which is conveyed through the car to the motor are infinitesimal; for the iron-work of the car affords a far better connection with the ground than the human body. If the current were conveyed by a broken wire to the wood-work of the car, the entire current from the most powerful dynamo would be stopped. As a proof of my assertion that the iron-work would conduct away the electricity and prevent the human body from receiving any of it, I need only mention the behavior of the stroke of lightning which descended the Eiffel Tower in Paris last August. A heavy bolt struck the tower, with a report which sounded like the discharge of a park of artillery. People at a distance from Paris saw the bolt descend, and the light of the discharge illumine the low-lying clouds as if the structure were suddenly enveloped in flames. There were four persons on the tower at the time, — assistants who had charge of different portions, — but no one received the slightest shock. The electric charge distributed itself through the iron-work of the tower, and the persons on the tower were as unconscious of its passing as birds which cluster on the overhead trolley wire are of the powerful current which is flowing under their feet. It is asked, however, Cannot the powerful magnetism of the motor beneath the flooring of the car affect our health? In answer to this inquiry, it may be said that none of our senses can detect the slightest effect from the most powerful magnetism. People have inserted their heads between the poles of a magnet which could lift a ton, and have perceived no effect. A blindfolded person cannot detect the attraction of a magnet which can draw a crowbar to itself with irresistible force. It has been maintained that certain persons see flame from magnets, but such persons are believed to be subject to hallucinations. It is safe to affirm that if a powerful state of magnetism existed in the car above the flooring the motor would not work.
The jar which one feels and the occasional shocks are mechanical, and not electrical. I was in an electric car lately which ran over a torpedo, placed on the track by some mischievous person. The car was immediately emptied, and many preferred to walk rather than to return to the car. What has been said in regard to the possible danger of receiving a shock from the electric current while in the car will serve to answer the inquiry whether there is not danger of being struck by lightning while riding on an electric railway. If a bolt from heaven should strike the overhead wire of the railway, it would find such an easy passage to the earth through the trolleys of the cars, through the motors, and thence to the rails, that the passengers would be in the condition of the assistants on the Eiffel Tower. It has never been proved that lightning is attracted by the electric currents which are flowing in the overhead wire.
When one leaves an electric car, however, there are possible dangers. I am inclined to believe that the lady who claims to have received a shock while getting into a rear car was mistaken, for the amount of shock which she could receive through gloved hands and leather shoes from even a “sneak” current could not be detected by the most delicate instruments. I notice that many persons carefully avoid treading on the rails of the electric railway. They can be assured that even if they should touch them with the bare hands no sensation would be felt; furthermore, one can touch the overhead trolley wire with bare hands with impunity if, at the same time, no connection is made with the ground. One can see, any day, laborers mounted on tall scaffolds, grasping the bare trolley wire while engaged in repairing it.
Wherein, therefore, consist the dangers to life from the overhead wire? Birds can rest upon it, men can touch it; it gives, while intact and continuous, no evidence of the mysterious influence contained in it save when the overhead trolley bounds up and down. Then there is a flash of lightning, as if some Prometheus burst into imprecations at man’s clumsy, device. The danger to life comes not from the steady flow of the current, but from its sudden cessation. Strange to say, it is not the steady burning of the fire, so much as the going out of the fire, which is deadly. The plain statement of fact, not clothed in scientific language, is this: If the overhead wire of the electric railway should break between the bare hands of a workman, he would be killed. It would be necessary, however, that the wire should be cut between the two bare hands with which he grasped the bare wire. The shock would then flow from shoulder to shoulder. The man’s life would cease with the current. If the wire should be cut beyond where it is held, — not between the hands, but beyond them both, — and if there should be no connection with the ground, no danger would result. If, standing on the ground, one should touch the rails of the electric railway, I have said that he would receive no shock. If this person should by any possibility touch the overhead wire and the rails at the same time, the instant he released his hold upon either he would receive a shock which I have no doubt would be a deadly one. When he releases his grasp the current suddenly stops between his arms, and he would be in a similar position to that of the workman who has hold of the two ends of a broken wire. Let us suppose that a telegraph or telephone wire has fallen upon the overhead wire of the electric railway, and that a person comes in contact with the dangling end of the wire. If the person should be standing in rubbers or dry shoes, it is not probable that he would receive a deadly shock from touching the wire, or from releasing his hold of it. If his shoes should be wet, however, in struggling to escape the wire he might receive a mortal injury. It is only at the moment of release that the rattlesnake would give its most deadly bite. It is maintained that horses are more sensitive to the electric current than men, and that this is the reason they are so frequently killed by the dangling wires which reach from the overhead wire to the street. It is much more probable that their iron shoes and their freedom from clothing make them for the moment better conductors of electricity than human beings, who are shod in rubber and leather and wear insulating garments.
The manner in which a horse is killed by a dead wire, that is, a wire which is out of use and whose only function is to be the means of death to some living creature, is therefore as follows: The dead wire falls upon a bare wire carrying a current; a horse runs into the wire, and contact is made with the ground and broken through the animal’s body. It is the breaking the connection which is deadly. In a blinding storm it would not be pleasant to find one’s self in the embraces of a dead wire. Yet with the present practice of allowing wires to cross the bare overhead wire of the electric railway, such embraces promise to be too common.
The dangers to life from the electric current in which the earth is not used are nothing if the circuit of the current is not broken. If the earth is used for the return circuit, the danger arises from breaking a connection between the metallic circuit and the earth. In the electric-car system, the current is sent out from the dynamo machine at the central station along the overhead wire, passes through the motor in each car to the rails, and then returns through the ground to the dynamo at the central station. The current constantly desires, so to speak, to escape to the ground from the overhead wire; and it seizes the opportunity afforded by any straggling wire which may fall on the overhead wire. Outside of cities and crowded streets of towns, the use of the earth as a return circuit is not dangerous, for wires are not liable to fall upon the overhead wire of the railway. In cities, however, the use of the earth as a part of the return circuit, I believe, is highly dangerous, both to life and to property.
The foregoing account of the danger to life from touching wires carrying a powerful electric current immediately raises the inquiry how strong a current is dangerous to life. The most contradictory statements have been made in regard to this point. The reason of the variance of the testimony resides in this: that the mere electrical pressure which is supplied, and the strength of current which flows through a circuit offering a certain resistance, do not determine the question whether the current is a killing one. It is the recoil in the sudden stoppage of a current which has been flowing through the coils of a dynamo that is deadly to life. This reflex action, which is due to induction, cannot be calculated from the electrical pressure supplied to the continuous circuit, or from the electrical current and the resistance. The current arising from induction, like a wave reflected from a rock, may have a higher crest than the incoming wave which produced it. The time rate, so to speak, of its change varies greatly with the coils in the circuit. When we hear, therefore, of a person taking with impunity one thousand volts, the volt being the electrical unit for pressure, we must ask how much current there was at this pressure, how many dynamo coils there were in circuit, and how great was the time rate of change at breaking the circuit. One can take the current from one hundred batteries, giving two hundred volts pressure, without serious discomfort, if there are no coils in the circuit. Interpose a powerful electro-magnet, and then break the circuit, the recoil current will make one feel as if he had been struck on the chest with a heavy sledge-hammer; the arms will draw up convulsively, the lips will strive to utter a cry of pain, and a sense of sinking, as in a fainting fit, will come over one. What I have portrayed from actual experience with two hundred volts pressure will give a lively sense of what would happen if a current of five hundred volts, running through dynamo coils, should be suddenly stopped in the human body: the recoil would be tremendous and deadly. It is related that a certain Mr. Jenkins, one evening, at a meeting of the Royal Institution, started Faraday on his celebrated researches upon electrical induction by asking why a shock was experienced when a circuit containing an electro-magnet was broken between the hands, and why no shock was felt when there was no coil or electro-magnet in the circuit. This inquiry was made fifty years ago, and Mr. Jenkins escaped an immortal name by not striving to answer the question for himself; for Faraday thereupon began the series of researches which have made his name famous. With electrical induction there is an end to life. With electrical induction, it may be said with truth, there is all end to our knowledge of electricity. How can this subtle fluid, this airy nothing, which travels on the ether of space, exhibit momentum, and rend obstacles like an express train in collision?
I suppose that the method of execution by electricity will be to break the current from a powerful dynamo between two points in the body of the criminal. It will be necessary to bring the bare skin, at two suitably separated points, in contact with the wire carrying an arc-light current, and then break the metallic circuit between these points. Interposing these points between the terminals of a wire carrying a to-and-fro electric current, that is a current which is sent first in one direction and then in the opposite, would have a similar effect to that produced by breaking a continuous current. The continuous current is like a snake, which strikes once and loses its fangs. The alternating current is a snake which can strike again and again. The latter current is coming into use in electric lighting, and it may yet be employed in the transmission of power. Theory indicates certain advantages in its use over that of the continuous current. The dangers from its employment are very great, and will need careful safeguards.
It is not, however, the possible risk to life in the contact with the ground and a dangling dead wire, which has come in contact with the overhead system of electric propulsion, that constitutes the most serious danger from electricity. What is most to be feared is the ease with which extensive fires can be started in cities by means of bare or poorly insulated electric circuits, of which the earth forms a portion. The electric current seeks to return to the generator which produces it by the path of least resistance. If, therefore, a telegraph or telephone wire, or any metallic conductor, should come in contact with a bare wire conveying a powerful current, this current would seek the ground by every possible way; and if the telegraph or telephone wire should be connected with the ground, the powerful current would be directed through telegraph or telephone instruments in offices and houses to ground connections. It is said, in reply to this view, that lightning frequently has entered houses by telephone and telegraph wires, and has merely burnt out a coil or fused a wire, and has not caused any serious conflagration. A sudden discharge through a circuit, however, is not so dangerous as a slow, insidious heating, which might go on for several hours before it is discovered. This heating could easily be produced by a portion of a powerful current leaking into houses and offices from a wire which has fallen upon a bare metallic circuit through which a current is flowing. What is to prevent, it may be asked, a great city being set on fire by electricity, in a hundred places at once, on the night of a blizzard? The inquiry is certainly not a frivolous one. The elements of danger are with us, and the questions of safeguards demand the most careful consideration by our municipal authorities.
The precautions now adopted are these: Safety wires not connected with any electric circuit are placed in some cases above the bare wires conveying powerful currents, to prevent any falling wire from reaching the latter. Fusible wires, made of an alloy of tin, are inserted in the telephone and telegraph circuits. These will melt at a comparatively low temperature, and any current more powerful than is customarily used upon the circuit will thus defeat its ends by burning out its own path. The fusible wire can be placed in a fireproof box. Another method, adopted in certain cases, is the employment of a ball of wax, which rests against the coils of the telegraph or telephone apparatus, and prevents a spring from touching a metallic connection. If the current in the coils should heat the coils, and therefore become dangerous, the wax melts, and the spring touches the metallic connection, and directs the current from the coils to the ground. This simple contrivance is not automatic, and endeavors have been made to arrange electro-magnetic instruments which shall divert currents to the ground when they reach a certain dangerous strength. All these devices can be made to work. Electricity is like a facile, mischievous boy, who, in his soft moods, can be safely entrusted with a delicate watch, a fragile Venetian vase, a glass model of a steam-engine; but there comes a moment when, if there is any possibility of man’s contrivances being upset, that possibility is discovered.
The use of a double overhead-wire system, that is of a complete metallic circuit, would obviate many dangers which now exist. This system would require two trolleys to each car. The electric current would flow along one wire, down one trolley, into the motor of the car, and then up through the second trolley, and return through the second overhead wire to the central station. In this way, the return through the earth would be obviated. But this system, of course, would require a heavy super-structure across the streets. There would then be two wires instead of one, which is used in the present overhead system.
There are certain mechanical and electrical difficulties, which, however, are not insuperable. With such a complete metallic circuit, there would be little danger from falling dead wires. One could touch one of the overhead wires and the ground with impunity, for no electricity would abandon the overhead wire for the ground, since it would prefer the metallic circuit for its return path to the central station. No horses would be killed by running into a dangling dead wire. The current would not be diverted into neighboring buildings, since it would have no excuse for seeking ground connections. If a wire should fall upon the overhead system, it would have no effect if it merely touched one wire. If it embraced both wires of this system, it would quickly burn and drop to the ground, incapable of doing any damage. In burning it would not convey the heat to neighboring buildings. If the double overhead wires should fall upon horses or people, no electrical shock would be received so long as the wires were not broken, and no shock would be received unless the wire happened to break between the limbs of the living creature upon which it might fall. This would be an unlikely conjunction of accidents. If the one overhead wire which is used at present should fall, the person or animal bridging the interval between it and the ground would be likely to receive a deadly shock in struggling to get free.
It may be said that the overhead electric-light systems now do not use the ground and have complete metallic circuits, yet we hear of men being burned to death, and of horses being killed by dead wires which touch the electric-light wires. These accidents result from defective insulation of the electric-light wires; and it must be confessed that such accidents are liable to happen even with complete metallic circuits that are above ground. A complete metallic circuit only mitigates the evil.
In general, electricity may be said to be the safest natural agency which man employs. Steam-boilers burst, and gas-mains explode. There is nothing explosive in an electric generator or an electric motor. The wires conveying the current can rend nothing, and become heated only through gross carelessness. The ease with which electric plants are installed testifies to the ready adaptability of electricity to man’s uses. This ease has a tendency to make electrical workingmen careless, and it also leads to the employment of ignorant persons.
In a neighboring museum, a skilled observer, engaged in studying the habits of rattlesnakes, is accustomed to put his arm into a tall jar containing the reptiles, and take them out with the bare hand. He has never been bitten, for he knows how to seize the snakes. The danger to an ignorant person in seizing an electric wire carrying a strong current is as great as that to which a person ignorant of the ways of snakes would be subjected, if he undertook to take the place of the skilled observer.