Motion is the ultimate object of science, and measures of
motion are many; but with thought as with matter, the true
measure is mass in its astronomic sense -- the sum or difference
of attractive forces. Science has quite enough trouble in
measuring its material motions without volunteering help to the
historian, but the historian needs not much help to measure some
kinds of social movement; and especially in the nineteenth
century, society by common accord agreed in measuring its
progress by the coal-output. The ratio of increase in the volume
of coal-power may serve as dynamometer.
The coal-output of the world, speaking roughly, doubled every
ten years between 1840 and 1900, in the form of utilized power,
for the ton of coal yielded three or four times as much power in
1900 as in 1840. Rapid as this rate of acceleration in volume
seems, it may be tested in a thousand ways without greatly
reducing it. Perhaps the ocean steamer is nearest unity and
easiest to measure, for any one might hire, in 1905, for a small
sum of money, the use of 30,000 steam-horse-power to cross the
ocean, and by halving this figure every ten years, he got back to
234 horse-power for 1835, which was accuracy enough for his
purposes. In truth, his chief trouble came not from the ratio in
volume of heat, but from the intensity, since he could get no
basis for a ratio there.
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