Though it is not very probable that any part of a tax, which is not only imposed upon one of the most proper subjects of taxation, a mere luxury and superfluity, but which affords so very important a revenue as the tax upon silver, will ever be given up as long as it is possible to pay it; yet the same impossibility of paying it, which, in 1736. made it necessary to reduce it from one-fifth to one-tenth, may in time make it necessary to reduce it still further; in the same manner as it made it necessary to reduce the tax upon gold to one-twentieth. That the silver mines of Spanish America, like all other mines, become gradually more expensive in the working, on account of the greater depths at which it is necessary to carry on the works, and of the greater expense of drawing out the water, and of supplying them with fresh air at those depths, is acknowledged by everybody who has inquired into the state of those mines. These causes, which are equivalent to a growing scarcity of silver (for a commodity may be said to grow scarcer when it becomes more difficult and expensive to collect a certain quantity of it), must, in time, produce one or other of the three following events: The increase of the expense must either, first, be compensated altogether by a proportionable increase in the price of the metal; or, secondly, it must be compensated altogether by a proportionable diminution of the tax upon silver; or, thirdly, it must be compensated partly by the one and partly by the other of those two expedients. This third event is very possible. As gold rose in its price in proportion to silver, notwithstanding a great diminution of the tax upon gold, so silver might rise in its price in proportion to labour and commodities, notwithstanding an equal diminution of the tax upon silver.