IMAGES are not arguments, rarely even lead to proof, but the mind craves them, and, of late more than ever, the keenest experimenters find twenty images better than one, especially if contradictory; since the human mind has already learned to deal in contradictions.
The image needed here is that of a new centre, or preponderating mass, artificially introduced on earth in the midst of a system of attractive forces that previously made their own equilibrium, and constantly induced to accelerate its motion till it shall establish a new equilibrium. A dynamic theory would begin by assuming that all history, terrestrial or cosmic, mechanical or intellectual, would be reducible to this formula if we knew the facts.
For convenience, the most familiar image should come first; and this is probably that of the comet, or meteoric streams, like the Leonids and Perseids; a complex of minute mechanical agencies, reacting within and without, and guided by the sum of forces attracting or deflecting it. Nothing forbids one to assume that the man-meteorite might grow, as an acorn does, absorbing light, heat, electricity -- or thought; for, in recent times, such transference of energy has become a familiar idea; but the simplest figure, at first, is that of a perfect comet -- say that of 1843 -- which drops from space, in a straight line, at the regular acceleration of speed, directly into the sun, and after wheeling sharply about it, in heat that ought to dissipate any known substance, turns back unharmed, in defiance of law, by the path on which it came. The mind, by analogy, may figure as such a comet, the better because it also defies law.
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. All ages of history have known high intensities, like the iron-furnace, the burning-glass, the blow-pipe; but no society has ever used high intensities on any large scale till now, nor can a mere bystander decide what range of temperature is now in common use. Loosely guessing that science controls habitually the whole range from absolute zero to 3000º Centigrade, one might assume, for convenience, that the ten-year ratio for volume could be used temporarily for intensity; and still there remained a ratio to be guessed for other forces than heat.
Since 1800 scores of new forces had been discovered; old forces had been raised to higher powers, as could be measured in the navy-gun; great regions of chemistry had been opened up, and connected with other regions of physics.
Within ten years a new universe of force had been revealed in radiation.
Complexity had extended itself on immense horizons, and arithmetical ratios were useless for any attempt at accuracy. The force evolved seemed more like explosion than gravitation, and followed closely the curve of steam; but, at all events, the ten-year ratio seemed carefully conservative. Unless the calculator was prepared to be instantly overwhelmed by physical force and mental complexity, he must stop there.
Thus, taking the year 1900 as the starting point for carrying back the series, nothing was easier than to assume a ten-year period of retardation as far back as 1820, but beyond that point the statistician failed, and only the mathematician could help. Laplace would have found it child's-play to fix a ratio of progression in mathematical science between Descartes, Leibnitz, Newton, and himself. Watt could have given in pounds the increase of power between Newcomen's engines and his own. Volta and Benjamin Franklin would have stated their progress as absolute creation of power. Dalton could have measured minutely his advance on Boerhaave. Napoleon I must have had a distinct notion of his own numerical relation to Louis XIV.
No one in 1789 doubted the progress of force, least of all those who were to lose their heads by it.
Pending agreement between these authorities, theory may assume what it likes -- say a fifty, or even a five-and-twenty-year period of reduplication for the eighteenth century, for the period matters little until the acceleration itself is admitted. The subject is even more amusing in the seventeenth than in the eighteenth century, because Galileo and Kepler, Descartes, Huygens, and Isaac Newton took vast pains to fix the laws of acceleration for moving bodies, while Lord Bacon and William Harvey were content with showing experimentally the fact of acceleration in knowledge; but from their combined results a historian might be tempted to maintain a similar rate of movement back to 1600, subject to correction from the historians of mathematics.