The rate of interest, though ultimately and permanently governed by the rate of profit, is however subject to temporary variations from other causes. With every fluctuation in the quantity and value of money, the prices of commodities naturally vary. They vary also, as we have already shewn, from the alteration in the proportion of supply to demand, although there should not be either greater facility or difficulty of production. When the market prices of goods fall from an abundant supply, from a diminished demand, or from a rise in the value of money, a manufacturer naturally accumulates an unusual quantity of finished goods, being unwilling to sell them at very depressed prices. To meet his ordinary payments, for which he used to depend on the sale of his goods, he now endeavours to borrow on credit, and is often obliged to give an increased rate of interest. This however is but of temporary duration; for either the manufacturer's expectations were well grounded, and the market price of his commodities rises, or he discovers that there is a permanently diminished demand, and he no longer resists the course of affairs: prices fall, and money and interest regain their real value. If by the discovery of a new mine, by the abuses of banking, or by any other cause, the quantity of money be greatly increased, its ultimate effect is to raise the prices of commodities in proportion to the increased quantity of money; but there is probably always an interval, during which some effect is produced on the rate of interest.
The price of funded property is not a steady criterion by which to judge of the rate of interest. In time of war, the stock market is so loaded by the continual loans of Government, that the price of stock has not time to settle at its fair level before a new operation of funding takes place, or it is affected by anticipation of political events. In time of peace, on the contrary, the operations of the sinking fund, the unwillingness, which a particular class of persons feel to divert their funds to any other employment than that to which they have been accustomed, which they think secure, and in which their dividends are paid with the utmost regularity, elevates the price of stock, and consequently depresses the rate of interest on these securities below the general market rate. It is observable too, that for different securities, Government pays very different rates of interest. Whilst 100_l._ capital in 5 per cent. stock is selling for 95_l._, an exchequer bill of 100_l._, will be sometimes selling for 100_l._ 5_s._, for which exchequer bill, no more interest will be annually paid than 4_l._ 11_s._ 3_d._: one of these securities pays to a purchaser at the above prices, an interest of more than 5-1/4 per cent., the other but little more than 4-1/4; a certain quantity of these exchequer bills is required as a safe and marketable investment for bankers; if they were increased much beyond this demand, they would probably be as much depreciated as the 5 per cent. stock. A stock paying 3 per cent. per annum will always sell at a proportionally greater price than stock paying 5 per cent., for the capital debt of neither can be discharged but at par, or 100_l._ money for 100_l._ stock. The market rate of interest may fall to 4 per cent., and Government would then pay the holder of 5 per cent. stock at par, unless he consented to take 4 per cent., or some diminished rate of interest under 5 per cent.: they would have no advantage from so paying the holder of 3 per cent. stock, till the market rate of interest had fallen below 3 per cent. per annum. To pay the interest on the national debt, large sums of money are withdrawn from circulation four times in the year for a few days. These demands for money being only temporary, seldom affect prices; they are generally surmounted by the payment of a large rate of interest.[36]