The practice where overhead conductors are employed, is to mount the converter box on a pole in the vicinity of the premises to be lighted, as shown by Fig. 13, and thus it is only necessary to lead the secondary or low potential wires into the building, the high potential wires remaining in an accessible position upon the pole. Fig. 14 is a view of North Street, Pittsfield, Massachusetts, engraved from a photograph, and shows a very neat form of tubular pole with its converter box on top. This arrangement is used throughout the city, and is a great improvement on the ordinary form of telegraph poles which so greatly disfigure American cities, and are really the most objectionable feature of the overhead wire system. [Illustration: Fig. 12.] [Illustration: FIG. 13.] [Illustration: FIG. 14. _To face page 37._] The potential ordinarily employed in the main circuits of the Westinghouse installations is about 1000 volts, and that in the lamp circuits 50 volts, the ratio of conversion, therefore, being as 20 to 1; the dynamos are manufactured, as a rule, in three sizes, No. 1 for 650, 16 candle-power lamps; Nos. 2 and 3 for respectively 1300 and 2500 lamps. The converters are also made in three ordinary sizes to supply 20, 30, and 40 lamps of 16 candle-power each. A 40-light converter contains about 85 pounds of iron and 25 pounds of copper, so that the total weight of metal is less than 3 pounds per lamp; the electrical efficiency of the converter is said to exceed 95 per cent. when the potential is reduced from 1000 volts in the primary to 50 in the secondary. “It is claimed that the trifling loss of energy in conversion from high to low potential at the point of consumption is made up for by gain at other points, especially in the increased efficiency of the lamps, so that an alternating current plant may be counted on to give 10-16 candle-power lamps per indicated horse-power, as against 7 with the direct system;” the comparative gain is doubtful, but by using 50 instead of 100 volts the life of the lamps is increased, the former having a much stronger filament and consequently a longer life. ELECTRIC MOTORS.