Then came another remarkably interesting contribution. Have you ever wondered why the pendulums of fine clocks were weighted with a gridiron of alternate rods of brass and steel? For purpose of ornament? Not at all—it constitutes a scientific solution of an embarrasing problem, due to the inevitable variations in temperature. Metals expand with heat and contract with cold. Notched iron bars can be made to "crawl" along a flat surface by alternately heating and cooling them. Bridge-builders sometimes arrange sliding points, or rocking points to adjust the differences in the length of the steel. Contraction and expansion are important factors in all their calculations. But a pendulum would change its rate of motion if it changed its length and this would interfere with its accuracy as a measurer of time. Graham worked upon this problem, too, and attached a jar of mercury to the rod of his pendulum for a weight. When the heat lengthened the rod, it also caused the mercury to rise, just as in a thermometer, and this left the "working-length" the same.
Such mercury-weighted pendulums are not uncommon to this day, but the more familiar gridiron came from the brain of John Harrison, who, in 1726, fixed the alternate rods in such a way that the expanding brass rods raised the weight as much as the expanding steel rods lowered it. Thus they neutralized each other.
The clock as we know it was now virtually complete. There were structural refinements, but no more radical improvements to be made. In tracing its development from the fourteenth to the eighteenth century, we note one curious likeness to the ancient history of recorded time. In this case, as before in Babylon, the people first concerned with the science were the priests, and after them the astronomers, but we note a still more important difference.
As the medieval passed into the modern, the practise of horology passed more and more out of the hands of scientists into the keeping of commercial workmen. The custodian of time was at first a priest, and finally a manufacturer. And this change was attended by a vast increase in the general use of timepieces, and the correspondingly greater influence of time upon society and men's way of living. The Middle Ages made clocks and watches; and clocks and watches make the age in which we live.
CHAPTER EIGHT
The Watch that Was Hatched from the "Nuremburg Egg"
In the second act of Shakespeare's play, As You Like It, when Touchstone, the fool, meets Jaques, the sage, he draws forth a sun-dial from his pocket and begins to moralize upon Time.
Touchstone's dial must have looked like a napkin-ring, with a stem like that of a watch, by which to hold it up edgewise toward the sun, and a tiny hole in the upper part of the ring through which a little sunbeam could fall upon the inner surface whereon the hours were marked. This pinhole was perhaps pierced through a slide, which could be adjusted up or down according to the sun's position at the time of year. In principle, therefore, it was a miniature of the huge dial of Ahaz of more than two thousand years before.
In another Shakespeare play, Twelfth Night, Malvolio is gloating in imagination over his coming luxury when he shall have married the heiress and entered upon a life of wealth and leisure.