Electric fire, phenomenon of electricity. [1] We observe the electric fire when electric matter has sufficiently gathered in an object and is directed in a manner such that it bursts and dazzles our eyes, traveling like lightning, so that it also burns, melts and consumes those objects that it is apt to consume, and then produces in these same objects effects resembling ordinary fire.

We also understand by the term electric fire that very quick and active fluid, present in various objects, and which penetrates them, and makes them move according to certain laws of attraction and repulsion which, in a word, demonstrates all the properties of electricity. This “fluid” is called “fire”, since its properties resemble those of elementary fire, among others, in that it shines in our eyes when it shoots with impulsiveness to enter or exit different bodies, to light inflammable substances, etc. See Fire.

We must therefore consider electric fire from two different points of view. Firstly, as a phenomenon of electricity, we will examine how it is produced, its power, how it is conducted, etc. Following this, we will consider it as a cause of electrical effects. We will also report the opinions of leading physicists on its nature and on the way in which it produces electrical phenomena.

Otto Guericke and Boyle have written that when certain electric objects were rubbed vigorously they glowed more or less brightly in the dark, and that some of them, such as diamonds, glowed for a considerable amount of time.  [2] We find in the collection of experiments by Hauksbee a series of very interesting observations on the light generated by several different bodies when rubbed against different materials, both outdoors and in the vacuum of an air-pump [machine pneumatique].  [3] However, since then physicists have regarded this light as mere phosphorescence, rather than the electric fluid made visible by the effects of friction.

It was as a result of the pain felt by Mr. Dufay when he accidently received a shock from the leg of person suspended by silk rope, that he surmised that the electric matter was an actual fire capable of burning as well as an ordinary fire, and that the sting he felt was in fact a burn.  [4] Finally, several scholars from Germany, having repeated the experiments of M. Dufay, continued his research. Mr. Ludolf has managed to ignite alcohol [ esprit de vin ] with an electric spark which he drew from the pommel of a sword, confirming by this fine experiment the hypothesis that Mr. Dufay had proposed on the resemblance between fire and electrical matter.

Today we know that all bodies that can conduct electricity — in other words, almost everything in nature — can make the electric fire manifest one way or another, once electrified to a certain degree. In bodies that are naturally electric, we need only to rub them slightly to produce this fire ; and after having thoroughly dried them out, the light they shine is durable. According to the nature of these various objects — diamonds, precious stones and glass—the light they generate is whiter, livelier, and has more brilliancy than that which can be generated by amber, sulfur, Spanish wax, resinous matter, or silk. But all these materials shine even more brightly when they are rubbed with substances that are not particularly electric, such as gilded paper, a hand, or woolen cloth, than when they are rubbed with silk, the skin of an animal (with hair), or even leather. But whatever materials are used to rub these electrified bodies, they render almost no light when the objects with which they are rubbed are not grounded, either immediately or by a sequence of non-electric bodies. For example, if a person on the floor vigorously rubs a glass tube, they will soon see it bursting with light: but if that person does the same thing, being mounted on a resin canvas sheet [i.e., not grounded], however vigorously they rub the tube, the light weakens, goes out, and does not reappear until the person stands on the floor again or if some non-electrical body grounded in the earth is put near them.

This light is more abundant and brighter when the rubbing is done in a vacuum, or in some hollow vessel from which all air has been removed by means of an air-pump. It may be said, in general, that electric fire is more easily manifested in a vacuum or semi-vacuum than in a space filled with air. Here are the proofs.

When a globe filled with air is rubbed against a cushion, both enclosed under the receptacle of an air-pump [i.e., a bell jar], this globe, after having its air evacuated, will generate bright and abundant light continuously, so long as the friction is maintained. The light weakens as the air returns, even if the globe is still rubbed with the same force. The same is true with an empty globe rubbed in the air. The slightest friction generates light in its interior, and this light gradually diminishes as soon as we introduce air into the globe. It is a rather general observation, that the light which is generated in a vessel void of any air, always appears brighter in the vessel and emanates from all points of the surface: it does not attach itself to the fingers [that is, there is no spark], when approached from a short distance, as it does ordinarily; it only becomes animated, and becomes livelier as the finger approaches, even some time after one has stopped rubbing. However, all the traits of light always tend to move towards the interior of the globe.

Electric fire spreads so easily in a vacuum that it is immediately excited in a recipient, or in any other vessel that is void of any air, by the mere approach of the tube or any other electrified body. It has been observed that this light was even brighter, when the air-voided vessels revolved on their axis, or were shaken by some sort of movement. When the two objects are at rest, the light fades gradually; but if the rubbed object is touched before it has entirely lost its electricity, the light comes back right away in the vacuum.

It is undoubtedly because of this capacity of the electric fire to manifest itself in a vacuum that we observe light at the top of a barometer when we electrify part of the downpipe by shaking the mercury: a thin tube, adequately purged of air, containing a couple of ounces of good dry mercury and that we shake in the dark. Indeed, a similar result is achieved when the bottle is well dried and purged of air and tapped simply from the exterior with the palm of the hand.

Of all these experiments conducted in a vacuum, there is none more interesting than the one conducted by Mr. Hauksbee on a 6-inch glass globe, coated around the middle from the inside with a wide band of melted sealing wax: this globe having been carefully emptied of all air, and applied to a rotation machine, allowed the ghostly outline [ fantôme lumineux ] of the hand rubbing it to be seen very distinctly on the concave surface of the globe, and this despite the opacity of the band of Spanish wax. The two poles left transparent allowed us to observe this phenomenon.

The fire emitted by animals, metals, and other electrified bodies is much stronger, more powerful and more direct than that emitted by a glass vase, a piece of amber, or a stick of sulphur. For example, an iron bar placed on silk cords and electrified by means of a glass tube generates a stronger spark, one that explodes with much more noise than that generated by the tube alone. And the more the volume and surface of these electrified bodies are increased, for example, by putting them in communication with one another by joining to this bar other large metallic surfaces, insulated in the same way, the bigger and brighter will be the spark generated when the electrified tube is brought into contact with it.

In general, this fire is that much brighter if the explosion is done with impetuosity; and the explosion is that much bigger the larger the quantity of electric matter that generates it. This is why if we apply an electric current from one or more well-rubbed glass tubes to very long and thick iron rods, the resulting sparks will be the liveliest, and like actual lightning, will travel noisily a considerable distance toward the hand [of the person carrying the tube], thus causing a sharp pain.

When a metallic object, or another body of the same nature, has acquired a static charge of a certain density through friction, the electric current that we continue to apply to it ultimately escapes, spreading light; sometimes in the form of a spark, similar to the ones generated by the touch of a finger; especially if the conductor only has obtuse angles and is rubbed in the proximity of a non-electric body. More commonly sparks appear to leap from the conductor’s uneven surface through a needle with an electrified tip, and the rays go in divergent directions as they separate from each other. These rays diverge more the stronger the electric current in the conductor. Their output is accompanied by a whisper and a murmur resulting from the effect with which it moves through the air. The matter exposed to these rays gives off a sulphurous smell, and red roses exposed to them for some time pale in colour.

By presenting a finger or any other non-electric object that is slightly pointed, to the plume that emerges from an electrified conductor, we will see another one form, but in the opposite direction, at the extremity of the object facing the conductor. The distance which this new plume moves varies not only following the density of the atmosphere of the conductor, but also following its shape as well as that of the body that is presented. The more the conductor is fixed, and the fewer angles there are, the greater the distance. The distance is even greater the more the object we approach is thin, sharp, or pointed. The closer we approach the finger to the conductor, or any pointed metal, the plumes become stronger more brilliant. They quickly condense when the distance is not great, and finally they form that spark which is so bright, so sudden, and so impetuous, that is so characteristic of lightening. The person who presents a finger feels the spark and some pain. The location where spark strikes is identified by a stinging, followed by a slight burning sensation.

It is with a similar flash of light that warm alcohol is ignited by presenting it in a metal spoon, at a blunt angle from the electric conductor: utilizing the same method, cannon powder and other combustible matters have been ignited.

But the electric fire that we have spoken of thus far is only a trifle compared to the one we can generate with the Leyden experiment. [5] Instead of a bottle, we used a large glass tile with both ends wrapped in tin exposing a two-inch band in the middle. This tile is placed on a metal stand, such that the lower strip of tin is in free communication with the earth. The top strip is then put in communication with the conductor by means of a chain connected to a conductor receiving the electric charge from globe. Once everything is in place the globe is vigorously rubbed, the glass tile is charged, just like the bottle in the Leyden experiment. And when communication between the two surfaces is established by means of a bent iron wire with blunt ends, and attached to the tip of a glass cane, a spark is produced of such intensity that the naked eye cannot bear to look at it, and whose explosion can be heard from afar. This spark pierces an entire hand [twenty-five sheets] of paper placed on the upper strip of tin, and which we bring into contact with the iron wire; it melts a sheet of gold leaf pressed between two glass plaques and arranged such that that the spark of the explosion passes through it, completing the circuit that passes from one strip to the other. The fusion is so complete, that the metal is found incorporated into glass to such a degree that it resists the action of the strongest solvents

This spark resembles thunder and lightening so strongly by its sparking effects that many physicists have had no difficulty in asserting that an explosion of thunder was nothing more than a very violent electric spark. We will examine this analogy more closely in the articles on Meteors and Thunder. We cannot however avoid advancing here that the storm clouds which pass fairly close to the earth electrify our iron bars insulated with wax so powerfully, that they generate sparks much stronger than the ones we can produce with our machines: that, in fact, it is this electric matter from the clouds that is behind Saint Elmo’s fire, sea funnels, and many other natural phenomena whose causes were unknown when we had but little knowledge of the electricity of clouds. See Electricity.

1. See Paola Bertucci, “Sparks in the dark: the attraction of electricity in the eighteenth century,” Endeavour 31 (August 2007): 88-93.

2. Otto von Guericke (1602 -1686): German scientist; Robert Boyle (1727-1691): English chemist.

3. Francis Hauksbee (1660–1713), Physico-Mechanical Experiments on Various Subjects: containing an account of several surprizing phenomena touching light and electricity (London, 1709).

4. Charles François de Cisternay du Fay (1698 – 1739) : French chemist.

5. So-called because the experiment with Leyden jars was first carried out at the University of Leyden. Leyden jars are the first form of electrical storage, and are known today as condensers or capacitors.