is threaded on both ends, and each end is provided with a brass, lead-covered bolt. The result of this arrangement is that when the bolts are drawn up tightly the lugs are clamped together, and if the joint is carefully made and kept tight it leaves nothing but lead exposed to the fumes of the acid. For general use this joint gives the best results of anything yet devised for the purpose.

A battery should always be protected by safety devices the same as a dynamo. Circuit breakers and fuses are both used for this purpose.

Section "a" of Rule 44 explains itself. It is a rule which has been often neglected in the past with disastrous results, the battery itself usually being the chief sufferer. It is, however, a rule that should be rigidly enforced.

$100

outs and safety devices in place in the above. Where ts, receptacles, and electroliers, etc., are connected, the above will be required. b. Ground wires for lighters of all classes, and ground detectors, must not be gas pipes within the building. c. Where telephone, r other wires connected with outside circuits are gether within any building, or where inside wires are uit or duct with electric light or power wires, the covh wires must be fire-resisting, or else the wires must in an air-tight tube or duct. d. All conductors contelephone, district messenger, burglar-alarm, waterric time, and other similar instruments, must be prohe point of entrance to the building with some protec(165)

tive device which will operate to shunt the instruments in case of a dangerous rise of potential, and will open the circuit and arrest an abnormal current flow. Any conductor normally forming an innocuous circuit may become a source of fire-hazard if crossed with another conductor, through which it may become charged with a relatively high pressure. (See Definitions.) The following formula for soldering fluid is suggested:

Saturated solution of zinc.

Alcohol.

Glycerine.

5 parts

.4 parts

..I part

DEFINITIONS. RULE 45. WIre Protectors:- Protectors must have a non-combustible, insulating base, and the cover to be provided with a lock similar to the lock now placed on telephone apparatus or some equally secure fastening, and to be installed under the following requirements: 1. The protector to be located at the point where the wires enter the building, either immediately inside or outside of the same. If outside, the protector to be inclosed in a metallic waterproof case. 2. If the protector is placed inside of building, the wires of the circuit from the support outside to the binding posts of the protector to be of such insulation as is approved for service wires of electric light and power, and the holes through the outer wall to be protected by bushing the same as required for electric light and power service wires. 3. The wire from the point of entrance to the protector to be run in accordance with rules for high potential wires; i. e., free of contact with building, and supported on non-combustible insulators. 4. The ground wire shall be insulated, not smaller than No. 16 B. & S. gauge. This ground wire shall be kept at least three (3) inches from all conductors, and shall never be secured by uninsulated double-pointed tracks. 5. The ground wire shall be attached to a water pipe, if possible; otherwise may be attached to a gas pipe. The ground wire shall be carried to and attached to the pipe outside of the first joint or coupling inside the foundation walls, and the connection shall be made by soldering, if pos sible. In the absence of other good ground, the ground shall be made by means of a metallic plate or a bunch of wires buried in a permanently moist earth.

MATERIALS:—The following are given as a list of non-combustible, non-absorptive, insulating materials and are listed here for the benefit of those who might consider hard rubber, fiber, wood, and the like, as fulfilling the above requirements. Any other substance which it is claimed should be accepted, must be forwarded for testing before being put on the market. 1. Thoroughly vitrified and glazed porcelain. 2. Glass. 3. Slate without metal veins. 4. Pure sheet mica. 5. Marble (filled). 6. Lava (certain kinds of). 7. Alberene stone.

WIRES:-The following list of wires have been tested and found to comply with the requirements for an approved insulation under Rule 10 (a), Rule 12 (d), and Rule 18 (a). Acme; Ajax; Americanite; Bishop; Canvasite; Clark; Columbia; Crescent; Crown; Edison Machine; Globe; Grimshaw (white core); Habirshaw (red core); Kerite; National India Rubber Co. (N. I. R.); Okonite; Paranite; Raven Core; Safety Insulated (Requa white core, Safety black core); Salamander (rubber covered); Simplex (caoutchouc); United States (General Electric Co.) None of the above wires to be used unless protected with a substantial braided outer covering.

We have already seen that wires of opposite polarity must be insulated from one another, and that all wires must be insulated from the ground. The question now arises: "What is insulation?" The term insulation is a relative one. Every conductor, even one of copper, offers a measurable resistance to a flow of current, and every insulator, even rubber, permits a measurable amount of electricity to pass through it. A wire covered with a thin covering of rubber may be well insulated to withstand a pressure of 100 volts, but poorly insulated for a pressure of 1,000 volts. What then is proper insulation? The insulating properties of the various rubber compounds used to cover wire vary very greatly when the insulation is new, and much more when the insulation is old; the covering of wires is

resistance of the

often injured or destroyed by the carelessness of workmen; and, again, every device attached to a circuit offers some opportunity for leakage. The thickness of insulation on wires cannot therefore be taken as a standard. The only practical standard is an electrical standard. In any system of conductors the insulation of the wires must present a certain resistance to the flow of current from the positive to the negative conductors, along any path, except the path provided by the wires themselves and the lamps, motors, etc., connected to them. This resistance is called the insulation system. It is measured in ohms. We must bear in mind that our electricity does not try to leak off into space or into the ground, but that whenever there is a difference of electrical pressure between two wires, this pressure is always trying to send a current from one wire to the other. The current which will flow depends upon the total resistance of all paths between the two wires. If the two wires come into metallic connection, they are as we say "crossed," and we have what is called a short circuit. If one of the wires comes into electrical contact with the earth, then that wire is "grounded;" we then have nothing separating the wires electrically except the insulation of the other wire. If now the second wire becomes connected electrically to the earth, we have the two wires connected electrically through the earth, and a leakage takes place. The amount of this leakage of course depends upon the resistance of the contacts between the wires and the earth. A ground on one wire is only dangerous as it is a step, half way, toward the crossing of