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Dyfyniad Arddull ChicagoUsher , Abbott Payson. A History of Mechanical Inventions. New York: McGraw-Hill, 1929.
Dyfyniad MLAUsher , Abbott Payson. A History of Mechanical Inventions. McGraw-Hill, 1929.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.