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10 MOTION PICTURE HANDBOOK Wiring. INSULATION. This is a matter of the UTMOST IMPORTANCE to which too little attention is usually paid. In too many in- stances current bills are excessive simply for the reason that there are unsuspected current leakages due to faulty insula- tion. By this it is not necessarily meant that the wire cover- ing is faulty. Insulation, in its true sense, means keeping the current from contact with the ground, in any degree, at all points, also keeping the opposite wires of a circuit from electrical contact with each other. We confine electricity to the wires by insulation, and the higher the pressure (voltage) the more perfect must be the insulation. If there be a small "pin-hole" in the seam of a boiler the steam will still be confined at pressure but some of it will be escaping, thus causing constant waste. If there be a slight imperfect "ground" (imperfect connection between the earth and the wire) there will be a small but constant current leakage, which will tell in the meter and therefore in the current bill. You will thus readily see the necessity for very carefully insulating your wires. Further along I will tell you how to detect grounds. Air is a conductor of electricity, but a very poor one. It will only carry current at enormous voltage—far in excess of anything used commercially, with the single exception of wireless telegraphy. Air may, therefore, be said, so far as commercial electric current is concerned, to be an absolute non-conductor, and it follows that current cannot escape from the wires by way of the air. Certain substances, such as rubber, glass, porcelain and others, are non-conductors of electricity, arid by stringing the wires through the air, allow- ing them to come in contact with nothing but non-conducting material, the current is confined to the wire, just as is the steam in a boiler by its steel plates and rivets. Wires are usually covered with rubber or some non-conducting compo-