Physics. [f. name of James Watt (1736–1819), the inventor of the modern steam-engine, and a pioneer in the science of energy.] A unit of activity or power (used chiefly with reference to electricity), corresponding to 107 ergs of work per second, to the rate of work represented by a current of one ampere under the pressure of one volt, or to 1/746 (= 0.00134) English horse-power.
1882. Siemens, in Rep. Brit. Assoc., Presid. Addr. 6. The other unit I would suggest adding to the list is that of power. The power conveyed by a current of an Ampère through the difference of potential of a Volt is the unit consistent with the practical system. It might be appropriately called a Watt, in honour of … James Watt…. A Watt, then, expresses the rate of an Ampère multiplied by a Volt, whilst a horsepower is 746 Watts, and a Cheval de Vapeur 735.
1882. Athenæum, 2 Sept., 310/2. Two of his [Dr. Siemens’s] units were unanimously approved—namely, (1) the watt, which is the rate of doing work when a current of one ampere passes through a resistance of one ohm, [etc.].
1886. Thurston, in Jrnl. Frankl. Inst., Oct., 265. It was judged that it might have been driven up to 300,000 watts with safety.
1887. Rep. Brit. Assoc., 208. The Watt is defined to be the work done per second by the ampère passing between two points between which the difference of electrical potential is one volt.
1889. Telegr. Jrnl. & Electr. Rev., 13 Dec., 665/2. The A type of Sunbeam lamp required only 2 watts per candle-power as compared with 31/2 watts for the Edison-Swann lamp.
b. Comb.: watt-hour, the work done by one watt in one hour; wattmeter, an instrument for measuring electric energy.
1887. Ayrton, Pract. Electr., 444. By the employment, however, of a ‘wattmeter,’ it is possible to measure the watts directly.
1888. Pall Mall Gaz., 24 Jan., 11/2. With 4,500 lamps of 16 candle-power,… at a charge of 1/2d. per lamp per hour, or eightpence per Board of Trade unit of 1,000 Watt hours … the income would be £11,250, irrespective of [etc.].
1892. J. Swinburne, in Min. Proc. Inst. Civ. Engin., CX. 15. The ordinary wattmeter as used in continuous-current work consists of a fixed and movable coil.
1907. E. Wilson & Lydall, Electr. Traction, I. 379. This can be converted into watt hours per ton mile thus.
1907. Athenæum, 20 July, 74/3. Mr. J. T. Irwin gave a demonstration of the uses of his hot-wire oscillographs and hot-wire wattmeters.
