Commodity money as a theoretical backing for federally issued "gold certificates" to substitute for the gold. Between 1933 and 1970 (when the U.S. officially left the gold standard), one U.S. dollar was technically worth exactly 1/35 of a troy ounce (889 mg) of gold. However, actual trade in gold bullion as a precious metal within the United States was banned after 1933, with the explicit purpose of preventing the "hoarding" of private gold during an economic depression period in which maximal circulation of money was desired by influential economists. This was a fairly typical transition from commodity to representative to fiat money,
The Aurum Film Encyclopedia through 1990 and a different set of appendices. Ten pages were added to the new edition, covering the few films produced during the years 1984 - 1990. This edition was reprinted in 1995. Published in 1984, "The Aurum Film Encyclopedia: Science Fiction", followed the history of the genre chronologically, from 1897 – 1983. Unlike the previous volume, silent genre titles are included, and even minor genre films are reviewed in the main text. Also unlike the first volume, Hardy mentions the names of the various critics who provided the reviews in the text, which in this book were Denis Gifford,