Increased intensity of labour means increased expenditure
 of labour in a given time. Hence a working-day of more intense labour is
 embodied in more products than is one of less intense labour, the length
 of each day being the same. Increased productiveness of labour also, it
 is true, will supply more products in a given working-day. But in this
 latter case, the value of each single product falls, for it costs less
 labour than before; in the former case, that value remains unchanged, for
 each article costs the same labour as before. Here we have an increase
 in the number of products, unaccompanied by a fall in their individual
 prices: as their number increases, so does the sum of their prices. But
 in the case of increased productiveness, a given value is spread over a
 greater mass of products. Hence the length of the working-day being constant,
 a day's labour of increased intensity will be incorporated in an increased
 value, and, the value of money remaining unchanged, in more money. The
 value created varies with the extent to which the intensity of labour deviates
 from its normal intensity in the society. A given working-day, therefore,
 no longer creates a constant, but a variable value; in a day of 12 hours
 of ordinary intensity, the value created is, say 6 shillings, but with
 increased intensity, the value created may be 7, 8, or more shillings.
 It is clear that, if the value created by a day's labour increases from,
 say, 6 to 8 shillings then the two parts into which this value is divided,
 viz., price of labour-power and surplus-value, may both of them increase
 simultaneously, and either equally or unequally. They may both simultaneously
 increase from 3 shillings to 4. Here, the rise in the price of labour-power
 does not necessarily imply that the price has risen above the value of
 labour-power. On the contrary, the rise in price may be accompanied by
 a fall in value. This occurs whenever the rise in the price of labour-power
 does not compensate for its increased wear and tear.