Man's physical universe

xanabras

314 FORMS OF ENERGY

cost $400 each, while, twelve years later, when 2,000,000 refrigerators

were manufactured, the price was only $163.

In 1914 a 60-watt electric-light lamp cost 43 cents, while a greatly

superior lamp cost only 10 cents in 1941.

Electric fans that cost $12.20 in

1914 could be replaced by superior

fans at $2.75 in 1938.

The first electric clocks sold for $30; by the time 2,500,000 a year

were being sold, the price dropped to $4.00.

One of the Most Significant Steps in Making Mass Production Possible

Was the Development of Interchangeable Parts.

Eli Whitney, inventor of the cotton gin, was largely responsible for

the evolution of the principle of interchangeable parts. In 1818 he

Fig. 105. Precision grinding one of the main parts of an electric locomotive.

Both the part and the abrasive wheel, which is under the hood to the left, are

rotated, the abrasive wheel at much higher speed. (Courtesy of the Westinghouse

Electric and Manufacturing Company.)

instituted the production of interchangeable parts for firearms.

America

has made such progress in the development of interchangeable parts

that this principle is known in Europe as the American system.

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