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clock is still in existence。 It is to be seen at the Museum of
Patents； South Kensington； and when we visited it a few months
ago it was going； and still marking the moments as they passed。
It is contained in a case about six feet high； with a glass
front； showing a pendulum and two weights。 Over the clock is the
following inscription：
〃This clock was made at Barrow； Lincolnshire； in the year 1715；
by John Harrison； celebrated as the inventor of a nautical
timepiece； or chronometer； which gained the reward of 20；000L。；
offered by the Board of Longitude； A。D。 1767。
〃This clock strikes the hour； indicates the day of the month； and
with one exception （the escapement） the wheels are entirely made
of wood。〃
This； however； was only a beginning。 Harrison proceeded to make
better clocks； and then he found it necessary to introduce metal；
which was more lasting。 He made pivots of brass； which moved
more conveniently in sockets of wood with the use of oil。 He
also caused the teeth of his wheels to run against cylindrical
rollers of wood； fixed by brass pins； at a proper distance from
the axis of the pinions； and thus to a considerable extent
removed the inconveniences of friction。
In the meantime Harrison eagerly improved every incident from
which he might derive further information。 There was a clergyman
who came every Sunday to the village to officiate in the
neighbourhood； and having heard of the sedulous application of
the young carpenter； he lent him a manuscript copy of Professor
Saunderson's discourses。 That blind professor had prepared
several lectures on natural philosophy for the use of his
students； though they were not intended for publication。 Young
Harrison now proceeded to copy them out； together with the
diagrams。 Sometimes； indeed； he spent the greater part of the
night in writing or drawing。
As part of his business； he undertook to survey land； and to
repair clocks and watches； besides carrying on his trade of a
carpenter。 He soon obtained a considerable knowledge of what had
been done in clocks and watches； and was able to do not only what
the best professional workers had done； but to strike out
entirely new lights in the clock and watch…making business。 He
found out a method of diminishing friction by adding a joint to
the pallets of the pendulum； whereby they were made to work in
the nature of rollers of a large radius； without any sliding； as
usual； upon the teeth of the wheel。 He constructed a clock on
the recoiling principle； which went perfectly； and never lost a
minute within fourteen years。 Sir Edmund Denison Beckett says
that he invented this method in order to save himself the trouble
of going so frequently to oil the escapement of a turret clock；
of which he had charge； though there were other influences at
work besides this。
But his most important invention； at this early period of his
life； was his compensation pendulum。 Every one knows that metals
expand with heat and contract by cold。 The pendulum of the clock
therefore expanded in summer and contracted in winter； thereby
interfering with the regular going of the clock。 Huygens had by
his cylindrical checks removed the great irregularity arising
from the unequal lengths of the oscillations； but the pendulum
was affected by the tossing of a ship at sea； and was also
subject to a variation in weight； depending on the parallel of
latitude。 Graham； the well…known clock…maker； invented the
mercurial compensation pendulum； consisting of a glass or iron
jar filled with quicksilver and fixed to the end of the pendulum
rod。 When the rod was lengthened by heat； the quicksilver and
the jar which contained it were simultaneously expanded and
elevated； and the centre of oscillation was thus continued at the
same distance from the point of suspension。
But the difficulty； to a certain extent； remained unconquered
until Harrison took the matter in hand。 He observed that all
rods of metal do not alter their lengths equally by heat； or； on
the contrary； become shorter by cold； but some more sensibly than
others。 After innumerable experiments Harrison at length
composed a frame somewhat resembling a gridiron； in which the
alternate bars were of steel and of brass； and so arranged that
those which expanded the most were counteracted by those which
expanded the least。 By this means the pendulum contained the
power of equalising its own action； and the centre of oscillation
continued at the same absolute distance from the point of
suspension through all the variations of heat and cold during the
year。＇5＇
Thus by the year 1726； when he was only thirty…three years old；
Harrison had furnished himself with two compensation clocks； in
which all the irregularities to which these machines were
subject； were either removed or so happily balanced； one metal
against the other； that the two clocks kept time together in
different parts of his house； without the variation of more than
a single second in the month。 One of them； indeed； which he kept
by him for his own use； and constantly compared with a fixed
star； did not vary so much as one whole minute during the ten
years that he continued in the country after finishing the
machine。＇6＇
Living； as he did； not far from the sea； Harrison next
endeavoured to arrange his timekeeper for purposes of navigation。
He tried his clock in a vessel belonging to Barton…on…Humber； but
his compensating pendulum could there be of comparatively little
use； for it was liable to be tossed hither or thither by the
sudden motions of the ship。 He found it necessary； therefore； to
mount a chronometer； or portable timekeeper； which might be taken
from place to place； and subjected to the violent and irregular
motion of a ship at sea； without affecting its rate of going。 It
was evident to him that the first mover must be changed from a
weight and pendulum to a spring wound up and a compensating
balance。
He now applied his genius in this direction。 After pondering
over the subject； he proceeded to London in 1728； and exhibited
his drawings to Dr。 Halley； then Astronomer…Royal。 The Doctor
referred him to Mr。 George Graham； the distinguished horologer；
inventor of the dead…beat escapement and the mercurial pendulum。
After examining the drawings and holding some converse with
Harrison； Graham perceived him to be a man of uncommon merit； and
gave him every encouragement。 He recommended him； however； to
make his machine before again applying to the Board of Longitude。
Harrison returned home to Barrow to complete his task； and many
years elapsed before he again appeared in London to present his
first chronometer。
The remarkable success which Harrison had achieved in his
compensating pendulum could not but urge him on to further
experiments。 He was no doubt to a certain extent influenced by
the reward of 20；000L。 which the English Government had off