and quickness of voyages, the preservation of ships and the lives
of men," and so on. The Act proceeds to constitute certain

persons commissioners for the discovery of the longitude, with
power to receive and experiment upon proposals for that purpose,

and to grant sums of money not exceeding 2000L. to aid in such
experiments. It will be remembered from what has been above

stated, that a reward of 10,000L. was to be given to the person
who should contrive a method of determining the longitude within

one degree of a great circle, or 60 geographical miles; 15,000L.
within 40 geographical miles; and 20,000L. within 30 geographical

miles.
It will, in these days, be scarcely believed that little more

than a hundred and fifty years ago a prize of not less than ten
thousand pounds should have been offered for a method of

determining the longitude within sixty miles, and that double the
amount should have been offered for a method of determining it

within thirty miles! The amount of these rewards is sufficient
proof of the fearful necessity for improvement which then existed

in the methods of navigation. And yet, from the date of the
passing of the Act in 1714 until the year 1736, when Harrison

finished his first timepiece, nothing had been done towards
ascertaining the longitude more accurately" target="_blank" title="ad.准确地；精密地">accurately, even within the wide

limits specified by the Act of Parliament. Although several
schemes had been projected, none of them had proved successful,

and the offered rewards therefore still remained unclaimed.
To return to Harrison. After reaching his home at Barrow, after

his visit to London in 1728, he began his experiments for the
construction of a marine chronometer. The task was one of no

small difficulty. It was necessary to provide against
irregularities arising from the motion of a ship at sea, and to

obviate the effect of alternations of temperature in the machine
itself, as well as the oil with which it was lubricated. A

thousand obstacles presented themselves, but they were not enough
to deter Harrison from grappling with the work he had set himself

to perform.
Every one knows the beautiful machinery of a timepiece, and the

perfect tools required to produce such a machine. Some of these
tools Harrison procured in London, but the greater number he

provided for himself; and many entirely new adaptations were
required for his chronometer. As wood could no longer be

exclusively employed, as in his first clock, he had to teach
himself to work accurately" target="_blank" title="ad.准确地；精密地">accurately and minutely in brass and other

metals. Having been unable to obtain any assistance from the
Board of Longitude, he was under the necessity, while carrying

forward his experiments, of maintaining himself by still working
at his trade of a carpenter and joiner. This will account for

the very long period that elapsed before he could bring his
chronometer to such a state as that it might be tried with any

approach to certainty in its operations.
Harrison, besides his intentness and earnestness, was a cheerful

and hopeful man. He had a fine taste for music, and organised
and led the choir of the village church, which attained a high

degree of perfection. He invented a curious monochord, which was
not less accurate than his clocks in the mensuration of time.

His ear was distressed by the ringing of bells out of tune, and
he set himself to remedy them. At the parish church of Hull, for

instance, the bells were harsh and disagreeable, and by the
authority of the vicar and churchwardens he was allowed to put

them into a state of exact tune, so that they proved entirely
melodious.

But the great work of his life was his marine chronometer. He
found it necessary, in the first place, to alter the first mover

of his clock to a spring wound up, so that the regularity of the
motion might be derived from the vibrations of balances, instead

of those of a pendulum as in a standing clock. Mr. Folkes,
President of the Royal Society, when presenting the gold medal to

Harrison in 1749, thus describes the arrangement of his new
machine. The details were obtained from Harrison himself, who

was present. He had made use of two balances situated in the
same plane, but vibrating in contrary directions, so that the one

of these being either way assisted by the tossing of the ship,
the other might constantly be just so much impeded by it at the

same time. As the equality of the times of the vibrations of the
balance of a pocket-watch is in a great measure owing to the

spiral spring that lies under it, so the same was here performed
by the like elasticity of four cylindrical springs or worms,

applied near the upper and lower extremities of the two balances
above described.

Then came in the question of compensation. Harrison's experience
with the compensationpendulum of his clock now proved of service

to him. He had proceeded to introduce a similar expedient in his
proposed chronometer. As is well known to those who are

acquainted with the nature of springs moved by balances, the
stronger those springs are, the quicker the vibrations of the

balances are performed, and vice versa; hence it follows that
those springs, when braced by cold, or when relaxed by heat, must

of necessity cause the timekeeper to go either faster or slower,
unless some method could be found to remedy the inconvenience.

The method adopted by Harrison was his compensation balance,
doubtless the backbone of his invention. His "thermometer kirb,"

he himself says, "is composed of two thin plates of brass and
steel, riveted together in several places, which, by the greater

expansion of brass than steel by heat and contraction by cold,
becomes convex on the brass side in hot weather and convex on the

steel side in cold weather; whence, one end being fixed, the
other end obtains a motioncorresponding with the changes of heat

and cold, and the two pins at the end, between which the balance
spring passes, and which it alternately touches as the spring

bends and unbends itself, will shorten or lengthen the spring, as
the change of heat or cold would otherwise require to be done by

hand in the manner used for regulating a common watch." Although
the method has since been improved upon by Leroy, Arnold, and

Earnshaw, it was the beginning of all that has since been done in
the perfection of marine chronometers. Indeed, it is amazing to

think of the number of clever, skilful, and industrious men who
have been engaged for many hundred years in the production of

that exquisite fabric--so useful to everybody, whether scientific
or otherwise, on land or sea the modern watch.

It is unnecessary here to mention in detail the particulars of
Harrison's invention. These were published by himself in his

'Principles of Mr. Harrison's Timekeeper.' It may, however, be
mentioned that he invented a method by which the chronometer

might be kept going without losing any portion of time. This was
during the process of winding up, which was done once in a day.

While the mainspring was being wound up, a secondary one
preserved the motion of the wheels and kept the machine going.

After seven years' labour, during which Harrison encountered and
overcame numerous difficulties, he at last completed his first

marine chronometer. He placed it in a sort of moveable frame,
somewhat resembling what the sailors call a 'compass jumble,' but

much more artificially and curiously made and arranged. In this
state the chronometer was tried from time to time in a large

barge on the river Humber, in rough as well as in smooth weather,
and it was found to go perfectly, without losing a moment of

time.
Such was the condition of Harrison's chronometer when he arrived

with it in London in 1735, in order to apply to the commissioners
appointed for providing a public reward for the discovery of the

longitude at sea. He first showed it to several members of the
Royal Society, who cordially approved of it. Five of the most

prominent members--Dr. Bailey, Dr. Smith, Dr. Bradley, Mr. John
Machin, and Mr. George Graham--furnished Harrison with a