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138 the functions of a machine. The former saw that what we gain in power we lose in space; while the latter went further, and saw that a machine, if left to itself, is strictly limited in the amount of work which it can accomplish, although its energy may vary from that of motion to that of position, and back again, according to the geometric laws of the machine.

192. There can, we think, be no question that the great development of industrial operations in the present age has indirectly furthered our conceptions regarding work. Humanity invariably strives to escape as much as possible from hard work. In the days of old those who had the power got slaves to work for them; but even then the master had to give some kind of equivalent for the work done. For at the very lowest a slave is a machine, and must be fed, and is moreover apt to prove a very troublesome machine if not properly dealt with. The great improvements in the steam engine, introduced by Watt, have done as much, perhaps, as the abolition of slavery to benefit the working man. The hard work of the world has been put upon iron shoulders, that do not smart; and, in consequence, we have had an immense extension of industry, and a great amelioration in the position of the lower classes of mankind. But if we have transferred our hard work to machines, it is necessary to know how to question a