THE Board of Trade electrical unit is the kilowatt-hour, which signifies a consumption of energy at the rate of 1,000 watts in an hour, or at a smaller rate for a corresponding longer time. The companys meter registers the units as they are consumed, and the householder pays accordingly.

A 40-watt lamp will run = 25 hours, while consuming one unit, at a cost of, say, 4d. Lamps of higher or lower power than this will keep alight respectively for shorter or longer times at the same cost; a 20-watt for 50 hours, a 100-watt for 10 hours, and so on.

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