Hence, as the use of machinery extends in a given industry, the
 immediate effect is to increase production in the other industries that
 furnish the first with means of production. How far employment is thereby found for an increased number of men, depends, given the length of the working-day and the intensity of labour, on the composition of the capital employed, i.e., on the ratio of its constant to its variable component.
 This ratio, in its turn, varies considerably with the extent to which machinery
 has already seized on, or is then seizing on, those trades. The number
 of the men condemned to work in coal and metal mines increased enormously
 owing to the progress of the English factory system; but during the last
 few decades this increase of number has been less rapid, owing to the use
 of new machinery in mining. [137] A new 418type of workman springs into life along with the machine, namely, its maker.
 We have already learnt that machinery has possessed itself even of this
 branch of production on a scale that grows greater every day. [138] As to raw material, [139] there is not the least doubt that the rapid strides of cotton spinning, not only pushed on with tropical luxuriance the growth of cotton in the United States, and with it the African slave trade, but also made the breeding of slaves the chief business of
 the border slave-states. When, in 1790, the first census of slaves was
 taken in the United States, their number was 697,000; in 1861 it had nearly
 reached four millions. On the other hand, it is no less certain that the
 rise of the English woollen factories, together with the gradual conversion
 of arable land into sheep pasture, brought, about the superfluity of agricultural
 labourers that led to their being driven in masses into the towns. Ireland,
 having during the last twenty years reduced its population by nearly one
 half, is at this moment undergoing the process of still further reducing
 the number of its inhabitants, so as exactly to suit the requirements of
 its landlords and of the English woollen manufacturers.