377. =Electrics and Non-Electrics.=--It will be observed, on looking over the list of conductors and non-conductors, that among the non-conductors are those substances in which electricity is easily excited by friction, such as glass, amber, silk, etc. These were therefore called electrics. The conductors, on the other hand, were called non-electrics, it being supposed that electricity could not be excited with them. But this has been found not to be true. For example, if a metal be insulated by being placed on a pillar of glass or of gumlac, so that the electricity, when excited, can not pass off readily, its generation can be made manifest. It is probably true that every substance is more or less an electric, it being difficult to make this manifest in the case of conductors, because the electricity passes off as fast as it is generated. 378. =Electricity Every Where Active.=--I have said that there is electricity in all substances, each having its own capacity for it, but that in the usual condition of substances the electricity is in a state of equilibrium, and therefore of quiet. We see this quiet disturbed whenever there is a thunder-storm, when we rub glass or silk, or a cat's back, or when we work an electrical machine. But the active state of electricity is not limited to such palpable demonstrations as these. Electricity is undoubtedly in action every where and always, although we can seldom appreciate and measure its action. Wherever there is motion there is a disturbance of the equilibrium of electricity, and a consequent return to this equilibrium. And this change from the one state to the other must be the constant cause of important changes and operations in the world around us, and in our own bodies. Let us look at some of the indications of this universality electrical action. The friction of any electric upon another awakens it. The friction of the belts upon the drums in cotton factories does it quite freely. Every stroke of India rubber upon paper as you erase a pencil mark excites electricity. The blowing of air upon glass does the same. So, also, does the blowing off of steam from an engine. Electricity has been excited even upon ice by rubbing it when cooled down to 13° below zero. Experiments upon the air have shown that there is usually some free electricity in it, the atmosphere being generally in a positive state, especially when the air is dry and clear. It is constantly generated from one source and another. It is generated every where by evaporation. Every gust of wind, causing friction of the particles of the air upon various substances, generates it. Motion of every kind probably generates it. Chemical action, as you will see in another part of this chapter, generates it every where. It is generated also in the operations of life, and in some animals there are special organs--electrical batteries--for the generation of this agent. [Illustration: Fig. 259.]