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."

"And whose scheme was that?"

"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