Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

proximity, or else by means of magnetism. That developed by the influence of the former is called electro-static or electro- dynamic induction, and also electro-magnetism; that of the latter is termed magneto-electric induction or magneto-electri- city. When two helices (which are, indeed, but coils or bobbins of wire in which galvanic currents are then flowing in the same direction) are placed end to end, they attract each other; but if one of them is reversed, so as to give opposite currents, repul- sion is manifested. So, according to Ampere's theory, when two permanent steel magnets are placed end to end, there is attraction or repulsion on the same principle. If we take a Smee's battery, or a good sized and active sul- phate of copper battery, and connect the poles by a short copper wire, no spark is usually perceived when the connection is formed or broken, but, if any, never at contact, and only very faint when opened. But if this connection wire is replaced by one that is fifty or a hundred feet long, the spark appears much brighter and more certain ; but if we coil this wire as on a spool, then the spark is still more vivid and more uniform. The most advantageous length of wire coil for producing the great- est spark depends upon the diameter and quality of the wire, and also upon the quantity and intensity of the battery. If a battery of higher intensity is employed, such as Grove's, then the wire may be much further increased; but the greater the quantity of the electric current, the shorter or larger must be this wire in order to transmit the whole of the current, and to obtain the greatest effector the brightest spark. By means of a wire some hundreds of feet in length, a slight shock may be felt from a single pair at the moment of opening the circuit, if its poles are arranged as moist electrodes, and are held in the hands. By testing it through the tongue, this intensity in- creases until the wire is some six or seven hundred feet long: by using a number of pairs, or even a smaller size, a greater length of wire in helix can be employed for shock or spark with greater effect. The maximum effects of a single small battery are, of course, less than those of a large one, and if the requi- site length of wire for the given battery current is exceeded, the effects are diminished.