Economists have little distinguished between the different forms of circuits, nor have they examined them individually with relation to the turnover of capital. They generally consider the form M ... M', because it dominates the individual capitalist and aids him in his calculations, even if money is the starting-point only in the shape of money of account.
Others start with outlays in the form of elements of production to the point when returns are received, without alluding at all to the form of the returns, whether made in commodities or money. For instance, "the Economic Cycle, . . . the whole course of production, from the time that outlays are made till returns are received. In agriculture, seedtime is its commencement, and harvesting its ending." S. P. Newman, Elements of Political Economy , Andover and New York, p. 81. Others begin with C' (the third form): Says Th. Chalmers, in his work On Political Economy , 2nd ed., Glasgow, 1832, p. 85 et seq.: "The world of trade may be conceived to revolve in what we shall call an economic cycle, which accomplishes one revolution by business, coming round again, through its successive transactions, to the point from which it set out. Its commencement may be dated from the point at which the capitalist has obtained those returns by which his capital is replaced to him: whence he proceeds anew to engage his workmen; to distribute among them, in wages, their maintenance, or rather, the power of lifting it; to obtain from them, in finished work, the articles in which he specially deals; to bring these articles to market and there terminate the orbit of one set of movements, by effecting a sale, and receiving, in its proceeds, a return for the whole outlays of the period."As soon as the entire capital-value invested by some individual capitalist in any branch of production whatever has described its circuit, it finds itself once more in its initial form and can now repeat the same process. It must repeat it, if the value is to perpetuate itself as a capital-value and to create surplus-value. An individual circuit is but a constantly repeated section in the life of a capital; hence a period. At the end of the period M ... M' capital has once more the form of money-capital, which passes anew through that series of changes of form in which its process of reproduction, or self-expansion, is included. At the end of the period P ... P capital resumes the form of elements of production, which are the prerequisites for a renewal of its circuit. A circuit performed by a capital and meant to be a periodical process, not an individual act, is called its turnover. The duration of this turnover is determined by the sum of its time of production and its time of circulation. This time total constitutes the time of turnover of the capital. It measures the interval of time between one circuit period of the entire capital-value and the next, the periodicity in the process of life of capital or, if you like, the time of the renewal, the repetition, of the process of self-expansion, or production, of one and the same capital-value.
Apart from the individual adventures which may accelerate or shorten the time of turnover of certain capitals, this time differs in the different spheres of investment. Just as the working day is the natural unit for measuring the function of labour-power, so the year is the natural unit for measuring the turnovers of functioning capital. The natural basis of this unit is the circumstance that the most important crops of the temperate zone, which is the mother country of capitalist production, are annual products. If we designate the year as the unit of measure of the turnover time by T, the time of turnover of a given capital by t, and the number of its turnovers by n, then n = T/t. If, for instance, the time of turnover t is 3 months, then n is equal to 12/3, or 4; capital is turned over four times per year. If t = 18 months, then n = 12/18 = 2/3, or capital completes only two-thirds of its turnover in one year. If its time of turnover is several years, it is computed in multiples of one year. >From the point of view of the capitalist, the time of turnover of his capital is the time for which he must advance his capital in order to create surplus-value with it and receive it back in its original shape. Before examining more closely the influence of the turnover on the processes of production and self-expansion, we must investigate two new forms which accrue to capital from the process of circulation and affect the form of its turnover.