all times requires 'the same sacrifice of toil and labour to produce it.'[325] The 'sacrifice' measures the 'utility,' and we may assume that the same labour corresponds in all ages to the same psychological unit. But, on the other hand, at any given period things will exchange in proportion to the labour of producing them. This follows at once from Ricardo's postulates. Given the single rate of wages and profits, and assuming the capital employed to be in the same proportion, things must exchange in proportion to the quantity of labour employed; for if I got the same value by employing one labourer as you get by employing two, my profits would be higher. Ricardo, indeed, has to allow for many complexities arising from the fact that very different quantities of capital are required in different industries; but the general principle is given by the simplest case. Hence we have a measure of value, applicable at any given time and in comparing different times. It implies, again, what M'Culloch sums up as the 'fundamental theorem,' that the value of 'freely produced commodities' depends on the quantity of labour required for their 'production.' What is made by two men is worth twice what is made by one man. That gives what M'Culloch calls the 'clue to the labyrinth.' The doctrine leads to a puzzle. If I can measure the 'sacrifice,' can I measure the 'utility' which it gains? The 'utility' of an ounce of gold is not something 'objective' like its physical qualities, but varies with the varying wants of the employer. Iron or coal may be used for an infinite variety of purposes and the utility will be different in each. The thing may derive part of its 'utility' from its relation to other things. The utility of my food is not really separate from the utility of my hat; for unless I eat I cannot wear hats. My desire for any object, again, is modified by all my other desires, and even if I could isolate a 'desire' as a psychological unit, it would not give me a fixed measure. Twice the article does not give twice the utility; a double stimulus may only add a small pleasure or convert it into agony. These and other difficulties imply the hopelessness of searching for this chimerical unit of 'utility' when considered as a separate thing. It shifts and escapes from our hands directly we grasp it. Ricardo discusses some of these points in his interesting chapter on 'Value and Riches.' Gold, he says, may cost two thousand times more than iron, but it is certainly not two thousand times as useful.[326] Suppose, again, that some invention enables you to make more luxuries by the same labour, you increase wealth but not value. There will be, say, twice as many hats, but each hat may have half its former value. There will be more things to enjoy, but they will only exchange for the same quantity of other things. That is, he says, the amount of 'riches' varies, while the amount of value is fixed. This, according to him, proves that value