The act is sometimes described as having called for a monthly issue of two million silver dollars; but this was not the exact situation. The amount of silver obtainable with two million dollars obviously varies according to the price of the metal in terms of the dollars with which the purchases are made. In February, 1878, when the first purchases were made, those dollars were the inconvertible United States notes, or greenbacks, worth something less than their face in gold. The amount of silver bullion obtainable with two million such dollars depended, on the one hand, on the price of silver bullion in terms of gold, and on the other hand on the value of the dollars themselves in terms of gold. When specie payments were resumed, on the first of January, 1879, and the greenbacks became redeemable in gold, the measure of value in the United States became gold, and the extent of the coinage of silver dollars under the act of 1878 became simply a question of how much silver bullion could be bought with two million dollars of gold. The price of silver in 1878 was, in terms of gold, not far from a dollar for an ounce of standard silver. Since 1878 it has gone down almost steadily, and ... in 1889 was barely above 80 cents an ounce.[19] The silver dollar of 412-1/2 grains contains less than an ounce (480 grains) of standard silver. The monthly purchase of two million dollars' worth of silver has therefore always yielded more than two million silver dollars, the amount being obviously greater as the price of silver went lower. On the average, the monthly yield [was] not far from two million and a half of silver dollars.... Thirty millions of silver dollars a year was roughly the addition to the currency of the community from the act of 1878. SILVER CERTIFICATES [20]An important provision of the act of 1878 was that authorising the issue of silver certificates against the deposit of silver dollars. This authority was limited at the time to certificates in denominations only of ten dollars and upward: a restriction which ... proved to be of great importance. At the time it does not seem to have been expected that the silver certificates would enter directly into the circulating medium; we may infer from the restriction to large denominations that no such expectation was entertained. But in fact, it has been chiefly in the form of certificates that the silver has entered into circulation. These certificates, it is true, are not, like the dollars themselves, a legal tender; but they are receivable for all public dues, customs included, and they pass from hand to hand at least as readily as the bulky pieces which they represent. CAUSES OF THE ACT