It is self-evident, that in proportion as the use of machinery
 spreads, and the experience of a special class of workmen habituated to
 machinery accumulates, the rapidity and intensity of labour increase as
 a natural consequence. Thus in England, during half a century, lengthening
 of the working-day went hand in hand with increasing intensity of factory
 labour. Nevertheless the reader will clearly see, that where we have labour,
 not carried on by fits and starts, but repeated day after day with unvarying
 uniformity, a point must inevitably be reached, where extension of the
 working-day and intensity of the labour mutually exclude one another, in
 such a way that lengthening of the working-day becomes compatible only
 with a lower degree of intensity, and a higher degree of intensity, only
 with a shortening of the working-day. So soon as the gradually surging
 revolt of the working-class compelled Parliament to shorten compulsorily
 the hours of labour, and to begin by imposing a normal working-day on factories
 proper, so soon consequently as an increased production of surplus-value
 by the prolongation of the working-day was once for all put a stop to,
 from that moment capital threw itself with all its might into the production
 of relative surplus-value, by hastening on the further improvement of machinery.
 At the same time a change took place in the nature of relative surplus-value.
 Generally speaking, the mode of producing relative surplus-value consists
 in raising the productive power of the workman, so as to enable him to
 produce more in a given time with the same expenditure of labour. Labour-time
 continues to transmit as before the same value to the total product, but
 this unchanged amount of exchange-value is spread over more use-value;
 hence the value of each single commodity sinks. Otherwise, however, so
 soon as the compulsory shortening of the hours of labour takes place. The
 immense impetus it gives the development of productive power, and to economy
 in the means of production, imposes on the workman increased expenditure
 of labour in a given time, heightened tension of labour-power, and closer
 filling up of the pores of the working-day, or condensation of labour to
 a degree that is attainable only within the limits of the shortened working-day.
 This condensation of a greater mass of labour into a given period thenceforward
 counts for what it really is, a greater quantity of labour. In addition
 to a measure of its extension, i.e., duration, labour now acquires a measure
 of its intensity or of the degree of its condensation or density. [75]387The denser hour of the ten hours’ working-day contains more labour, i.e., expended labour-power than the more porous hour of the twelve hours’ working-day. The product therefore of one of the former hours has as much or more value
 than has the product of 1 1/5 of the latter hours. Apart from the increased
 yield of relative surplus-value through the heightened productiveness of
 labour, the same mass of value is now produced for the capitalist say by
 3 1/3 hours of surplus-labour, and 6 2/3 hours of necessary labour, as
 was previously produced by four hours of surplus-labour and eight hours
 of necessary labour.