The growth of machinery has acted as an enormous stimulus to the study of natural laws. A larger and larger proportion of human effort is absorbed in processes of invention, in the manipulation of commerce on an increasing scale of magnitude and complexity, and in such management of machinery and men as requires and educates high intellectual faculties of observation, judgment, and speculative imagination. Of that portion of workers who may be said, within limits, to control machinery, there can be no question that the total effect of machinery has been highly educative. The growing size, power, speed, complexity of machinery, undoubtedly makes the work of this class of workers "more intellectual." Some measure of these educative influences even extends to the "hand" who tends some minute portion of the machinery, so far as the proper performance of his task requires him to understand other processes than those to which his labour is directly and exclusively applied. So likewise consideration must be taken of the skilled work of making and repairing machinery. The engineers' shop and other workshops are becoming every year a more and more important factor in the equipment of a factory or mill. But though "breakdowns" are essentially erratic and must always afford scope for ingenuity in their repair, even in the engineers' shop there is the same tendency for machinery to undertake all work of repair which can be brought under routine. So the skilled work in making and repairing machinery is continually being reduced to a minimum, and cannot be regarded, as Professor Nicholson is disposed to regard it, as a factor of growing importance in connection with machine-production. The more machinery is used, the more skilled work of making and repairing will be required, it might seem. But the rapidity with which machinery is invading these very functions turns the scale in the opposite direction, at any rate so far as the making of machinery is concerned. Statistics relating to the number of those engaged in making machinery and tools show that the proportion they bear to the whole working population is an increasing one; but the rate of this increase is by no means proportionate to the rate of increase in the use of machinery. While the percentage of those engaged in making machinery and tools rises from 1.7 in 1861 to 1.8 in 1871 and 1.9 in 1881, 2.0 in 1891, the approximate increase of steam-power applied to fixed machinery and locomotives shows a much more rapid rise,--from 2,100,000 horse-power in 1860 to 3,040,000 in 1870 and 5,200,000 in 1880.[214] Moreover, an increased proportion of machinery production is for export trade, so that a large quantity of the labour employed in those industries is not required to sustain the supply of machinery used in English work. In repairs of machinery, the economy effected by the system of interchangeable parts is one of growing magnitude, and tends likewise to minimise the skilled labour of repair.[215]