Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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To be understood, this denomination of dynamic is given to that state of movement in which the two electricities are supposed to be, when travelling towards each other to neutralize, in con- tradistinction to the static state, or that of rest, as where these two different electricities are found when they are separately accumulated, on insulated bodies. This latter state is also called electric tension. We see, then, that dynamic electricity may be only instanta- neous, or it may be continuous. In the preceding case it was instantaneous, and done. But suppose one ball to be in com- munication with a constant source of positive electricity, while the other ball is connected with an equally constant source of negative electricity; the two electricities being constantly re- newed as fast as they are neutralized, there will be a continuous succession of sparks, if the balls or electrodes are brought only close together; but if so as to touch each other, then there will be between the two ball electrodes a continual, uninterrupted neutralization, or, in other words, a continuous reunion of the two electricities. This is denominated the continuous dynamic state, and also called the electric current. Electric Conduction. The property which is possessed by most bodies, and by metals in particular, of more or less readily acquiring and propagating through their whole extent the electricity that is possessed by that part of an electrized body with which they are in contact, is termed electric conduction, and such materials are called con- ductors. Those which do not possess this property are called insulators. The human body, ordinary wood, animals, vegeta- bles, and most minerals are conductors; while amber, wax, glass, baked hard wood, fur, gum-lac, resins, and a majority of crystals, as also silk, oil, rubber, and gutta percha are non- conductors, or, in other words, are insulators. The earth is our largest conductor ; the vast extent of atmospheric air over its sur- face, when dry, is our largest insulator. The diamond is the most perfect insulator, while silver is most nearly a perfect conductor.