But the fact is that we cannot distinguish so easily as we may seem to do between fixed and circulating capitals; there may be kinds of capital which are neither quite fixed nor quite circulating, but something between the two. Flour is soon eaten up, and is circulating capital. A flour mill lasts fifty years, perhaps, and may certainly be called fixed capital; a flour sack lasts about ten years on an average. Is such a sack fixed or circulating capital? It seems to me difficult to say. In the case of a railway, the coal and oil wanted for the engine are used up at once, and are clearly circulating capital; the railway wagons last about ten years, the locomotive engines twenty years or more; the railway stations last at least thirty years; there is no reason why the bridges and tunnels and embankments should not last hundreds of years with proper care. Thus we see that #capital is altogether a question of time, and we must say that capital is more fixed as it endures or continues useful a longer time; it is more circulating in proportion as it is sooner worn out or destroyed, and thus requires to be more frequently replaced#. #35. How Capital is obtained. Capital is the result of saving or abstinence#, that is, it can only be obtained by working to produce wealth, and then not immediately consuming that wealth. The poor savage who has to labour hard every day for fear that he may have to go without food, has no capital; but when he has food in hand, and can employ himself in making bows and arrows to facilitate the capture of animals, he is investing capital in the bows and arrows. Whenever we work in this way for a future purpose, we are living on capital and investing it. The abstinence (Latin, _abs_, from, and _tenens_, holding) consists in holding off from the enjoyment of something which we have produced, or might produce with the same labour. #To save# is to keep something whole or untouched for future use; we save it as long as we do not consume it. If I have a stock of flour and eat it up, there is an end of the flour, and I cannot be said to save that. But if, while eating the flour, I am engaged in making a plough or a cart, or any other durable thing which will help me in production, I have turned one form of capital into another form. I might have eaten the flour in idleness, in which case it would not have been capital. But, while eating it, I worked for a future purpose. In so doing I am said to #invest capital#, which means #to turn circulating into fixed capital, or less durable into more durable capital#. Capital, accordingly, is invested for longer or shorter periods according to the durability of the form in which it is invested (Latin, _in_, on, and _vestire_, to clothe). A good plough will perhaps last twenty years; all through that time the owner should be getting back by its use the benefit of the labour and capital spent in making it. When it is worn out, he ought to have all the capital it cost paid