This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Electricity excited by friction is usually denominated static, conveying the idea that it is stationary or not in action, while in the form of galvanism it is said to be dynamic, as being essentially in movement, and exercising power. Though this distinction is not very precise, it may serve at least the purposes of nomenclature. A very great difference exists between the phenomena exhibited by these two forms of electricity; the static having in a high degree the properties of attraction and repulsion, and, when brought into movement, exercising great mechanical power; the dynamic exhibiting its energy more in developing heat, and producing chemical change. It is supposed that this difference depends, not on any essential diversity of character, but on the different states of the electricity developed in the two methods; that excited by friction having little quantity, but great tension or intensity, by which it is able to overcome resistance, while that set in movement by contact and chemical reaction has feeble tension, but large quantity. These terms, however, are rather conventional, intended to represent certain qualities in convenient language, than absolutely expressive of the fact; for it is by no means universally admitted that electricity is a distinct substance, to which the term quantity is at all applicable, unless as a figure of speech.
Static electricity is developed by means of friction between two substances, and this is usually effected by an apparatus called the electrical machine, constructed in different methods, for an account of which I must refer to works on chemistry or natural philosophy. To every machine is attached an insulated conducting body called the prime conductor, which receives upon its surface the electricity as it is excited, and retains it for a considerable time, in consequence of the non-conducting property of the dry air around it. Thus developed, the electricity acquires a degree of tension, proportionate to the power and working of the apparatus, by which it is enabled to break its way through the resisting air to neighbouring bodies, producing a stream of light in its passage, and a very perceptible sound. When the tension is very great, the spark, as this flash is called, may be many inches long; when very slight, it may be even less than an inch. In order that the electricity may escape in this way, the body approaching the conductor must be rounded or flat; as, if pointed, it receives the electricity quietly, and almost insensibly from the conductor.
If any part of the person be brought into contact with the prime conductor, the electricity passes silently into and through it, or along its surface, into the earth, in search of the equilibrium to which it always tends.
If, instead of coming into absolute contact with the excited prime conductor, a part of the body be made to approach it within a certain distance, greater or less according to the degree of electric tension, the fluid passes to the body by sparks, which produce a decided sensation as they are received. By means of rods or chains of metal, or other conducting substance, in contact at one end with the prime conductor, and having a rounded knob at the other, the electricity may be conveyed to any convenient distance from the machine, and applied by sparks to any part of the body. These communicating instruments are called directors, and must be insulated from the hand of the operator by some non-conducting substance, such as glass, which may at the same time serve as a handle.
Another method of applying static electricity is by placing the patient upon a stool, insulated by glass legs, and then connecting him with the prime conductor. His body thus shares the electricity with the conductor, and acquires precisely the same relations towards the machine and other surrounding objects. In this way it may become saturated with the fluid, which escapes very slowly and silently from the hairs, finger and toe nails, and the surface of the body generally; the hairs rising up and standing apart under its repellent force. Sparks may now be drawn from any part of the body by the approach of a blunt conducting substance; and, by keeping the machine constantly in action, this condition may be indefinitely prolonged. By communicating with the negatively excited, instead of the positive prime conductor, it is obvious that the body may itself become negatively excited; and, by varying the connection, the peculiar effects of either of these two modes of the electric influence may be separately obtained. This method of applying electricity is denominated the electric bath.
This is a current of electricity directed to any part of the body, through the air, by means of a pointed insulated director, connected at one end with the excited prime conductor by a chain, and, at the other and pointed extremity, held near, but not in contact with the portion of surface to be acted on. The electricity silently and invisibly issues from the point, and, expanding cone-like as it passes through the air, spreads itself out broadly upon the surface. Exactly the reverse takes place, when a similar point is held near the body, itself in a state of electric excitation upon an insulated stool. Little if any sensation is in either case experienced.
By these instruments the greatest force of the electricity of friction is obtained. The jar is a broad-mouthed glass bottle, coated within and without by tin-foil, excepting the upper part of both surfaces, where it is bare. With the inner coating is in contact a chain, connected with a metallic rod, which passes upward through a cork, or other material closing the mouth of the bottle, and ends in a round metallic ball at top. When this ball is put in communication with the excited prime conductor of the machine, the inner coating becomes positively charged, while, at the same time, by the laws of electric induction, the outer coating passes into the negative or opposite state. If now a conducting substance be connected with the inner coat by means of the knob, and directly or indirectly with the outer, the equilibrium is instantly restored, and the whole force of the movement is exerted upon the connecting material. If this be the body, a shock is felt, proportionate in degree to the extent of the coated surfaces, and the amount of the charge. It may be so slight as to occasion little inconvenience, or so powerful as to destroy life like a flash of lightning, which, indeed, is nothing more than the spontaneous discharge of an analogous electric arrangement in the atmosphere, or between that and the earth. But to obtain a shock of such extreme violence, it would be necessary to make the bottle of an unwieldy magnitude; and the same end is attained by connecting together a number of bottles by their inner and outer surfaces respectively, so that the whole may be discharged at once. Such an arrangement is called the electric battery, and affords an instrument of immense power.
The current of electric force may, with either the jar or battery, be made to penetrate through the skin, and enter deeply into the body; and, by means of directors connected with the opposite excited surfaces, may be conveyed from one end of the body to the other, or through it from side to side, or from one part to another of a limb, or through very limited portions of the body, at the pleasure of the operator. The directors must of course have insulated handles, and their knobbed free extremities must be applied at the opposite extremities of the part through which the current is to pass. If the object be to direct the electricity into a single muscle, both extremities, as directed by M. Duchenne, should be applied immediately over the muscle, with the space of an inch or more between them.
A repetition of graduated effects may be obtained through the jar, by placing its ball in communication with the excited prime conductor, and its external surface, in any convenient method, with one of Lane's electrometers, in such a manner, that the ball of the electrometer shall not be in absolute contact with it, but within striking distance of the electrical spark. By means of chains, insulated directors may be connected with the prime conductor and the electrometer, and their knobs applied at the required points of the surface. When the machine is set in motion, and the jar becomes charged, at the moment of connection through the body, the electrical current passes between the knob of the electrometer and the outer coating of the jar, to establish the equilibrium. If the intervening space is large, the shock will be necessarily severe, for great tension will be necessary to overcome the resistance of the air; if very small, the shock may be slight; so that its severity may be regulated by regulating this interval, and at the same time attending to the working of the machine. Care should be taken that the jar should be fully discharged before commencing operations; and then the handle of the machine should be turned more or less frequently, and more or less rapidly, according to the effect required.