“(12.) Bare wires passing over the tops of houses should never be less than seven feet clear of any part of the roof, and they should invariably be high enough, when crossing thoroughfares, to allow fire-escapes to pass under them.
“(13.) It is most essential that the joints should be electrically and mechanically perfect. One of the best joints is that shown in the annexed sketches. The joint is whipped around with small wire, and the whole mechanically united by solder.
“(14.) The position of wires when underground should be efficiently indicated, and they should be laid down so as to be easily inspected and repaired.
“(15.) All wires used for indoor purposes should be efficiently insulated.
“(16.) When these wires pass through roofs, floors, walls, or partitions, or where they cross or are liable to touch metallic masses, like iron girders or pipes, they should be thoroughly protected from abrasion with each other, or with the metallic masses, by suitable additional covering; and where they are liable to abrasion from any cause or to the depredations of rats or mice, they should be efficiently encased in some hard material.
“(17.) Where wires are put out of sight, as beneath flooring, they should be thoroughly protected from mechanical injury, and their position should be indicated.
“N.B.—The value of frequently testing the wires cannot be too strongly urged. It is an operation skill in which is easily acquired and applied. The escape of electricity cannot be detected by the sense of smell as can gas, but it can be detected by apparatus far more certain and delicate. Leakage not only means waste, but in the presence of moisture it means destruction of the conductor and its insulating covering by electric action.”
The lamps may take either the “arc” form, or the “incandescent.” The former is produced by the electric current passing between carbon points, and requires considerable electrical pressure; they give a light of from 1500 to 4000 candle power; the mechanism of arc lamps has to be of the most delicate kind to ensure the proper distance of the carbon points being maintained. The lamps should be guarded by globes of frosted glass, not only to prevent incandescent pieces of carbon from falling, but to lessen the glare of the light. “Incandescent” lamps are of small size, giving a light of from 8 to 50-candle power, which is produced by the heating of a filament of carbon in a vacuum owing to the resistance caused to the electric current by this contraction of the conductor.
(3.) With regard to the value of the light produced, and its adaptability to the requirements of any town, it will be seen on reference to the opening of this chapter that at present considerable doubt exists as to its adaptability for general public lighting, and as each town varies in the length, straightness, and width of its streets, the number of its large squares or confined courts and alleys, the surveyor must use his own judgment as to the suitability of the light before recommending his corporation to adopt it.