"Advertising was primitive in those days," agreed McPhearson. "Sometimes when trade was dull the unfortunate apprentices were sent out to tour the streets and bring in customers. Or the present of a watch or clock would be made to the king or some nobleman of wealth and influence in the hope that such a gift would stimulate others to buy. No doubt even the celebrated Graham, in the days of his apprenticeship to Tompion, may have had some of these humble duties to perform. But if so they failed to dash his enthusiasm for his profession, for you see how well he profited by his teaching and what a master at clockmaking he finally became. He had always been an ingenious fellow interested in evolving mathematical instruments of all sorts."
"Were his clocks as good as Tompion's?" queried Christopher.
"As to that, the two were pretty well matched," was the answer. "Graham, however, concentrated most of his skill on watches while Tompion put the major part of his talent into long-case clocks which were unrivaled. For, by this time, with the gradual development and improvement of clock machinery, it was possible to make grandfather, or long-case, clocks that kept excellent time. The defects of the old wheel escapement of the thirteenth, fourteenth, and fifteenth centuries were, as I told you, remedied in part by the invention of the fusee, a device for equalizing the movement. Then came the conversion of such clocks into pendulum clocks—no very difficult matter. One of the balls on the verge was removed, thereby making the verge longer and increasing the weight of the other ball. Then such clocks, together with those having a crown wheel escapement, went in turn out of vogue and the anchor escapement ushered in what is commonly known as the grandfather clock. It was in producing this particular type of timepiece that Tompion and Graham excelled. The pendulum was hung from a thin steel spring instead of being placed on an axis carrying pallets and could swing without friction."
"It is generally conceded that a Dutchman by the name of Fromanteel brought the modern pendulum idea into England. You will recall that early in clock history there were some pendulums of a very unsatisfactory nature in use—pendulums that were regulated by weights and dangled at the back or across the front of old brass clocks."
"I remember, yes."
"Well, it was that same pendulum principle carried to greater perfection and now scientifically applied which made the present grandfather, or long-case, clock possible. Certainly Fromanteel did a vast service to English clockmaking when he brought this solution of the pendulum problem to London, for with the anchor, or dead-beat escapement, combined with a long pendulum terminating in a heavy bob, the force of gravity caused such slight variation that the motion was practically harmonic and had only a very minor effect on the clock. For a long case, you see, has an exceedingly confined arc of oscillation because the swing of the pendulum is so limited. It is this length of pendulum together with its almost harmonic motion which results in the excellent time-keeping done by clocks of the "grandfather" class. The time a pendulum takes to vibrate always depends on its length—that is, the distance between the center of suspension and the center of gravity of the bob."
McPhearson paused to hold to the light a small brass pivot he was filing.
"Just here," continued he, "we stumble upon still another of the multiple tribulations of the clockmaker. If a big clock is expected to do any very fine work the latitude of the place in which it is to be put must be taken into consideration. For example, experiment has proved that the length of a pendulum vibrating seconds at London will not serve as accurately in other latitudes, because according to the laws of gravity the length of seconds increases in a specific ratio as we advance from the equator toward the poles. The clockmaker must, therefore, take care to regulate the length of his pendulum to correspond with this law."
"Great Scott! Why, I never dreamed there was so much to clockmaking!" gasped the astonished Christopher.