In the case of _different_ countries, at the same time, the difficulties are not quite the same. Exchange is there determined not by labour but by money prices; and money is of very different value in the one country and in the other. But the differences in the value of money in different countries are in proportion to the different prices of agricultural labour—1500 days’ labour at 4_d._ a day in India, at 2_s._ in England, meaning £25 and £150 respectively; and, if fixed capital to the value of 300 days’ labour were advanced to each of them, while profits calculated in days’ labour were twenty per cent. in the one case, ten in the other, the result would be an article whose conditions of supply would require in the one case a money price of £31, in the other of £168. The difference is no doubt due to the superior efficiency of English industry and skill which enables England to purchase the precious metals more cheaply,[588] but the cost of getting the money would not tell us the true present value of the money in England or in India. It is not the labour spent on the gold, but the labour purchased by it, that will help us here. In each country within itself we would measure the natural value of money as well as of anything else by what labour it will purchase; know the difference between the value of money in the one and its value in the other by the difference between the amount of labour it will purchase in the one case and the amount it will purchase in the other.[589]