* B. & S. is the abbreviation for Brown and Sharp -the name of the standard wire gage in this country.

** A Mil equals one-thousandth of an inch.

†A Circular Mil is the unit of area when considering the cross-section of a wire; it is the area of a circle whose diameter is one mil, and is, therefore, equal to 0.000000785 square inch.

* Concealed Work is wiring composed of insulated conductors inclosed in a tube or molding, and not exposed to the air.

**Open Work is wiring composed of weatherproof insulated conductors exposed to the air.

Resistance of Copper increased 0.21 per cent. for each degree Fahrenheit increase of temperature.

*B. W. G. is the abbreviation for Birmingham wire gage--an English wire gage differing but slightly from the B. & S. gage.

E. B. B. is the abbreviation for the "Extra Best Best" grade of iron wire.

B. B. is the abbreviation for the "Best Best" grade of iron wire.