in 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 offered for an instrument that should enable
the longitude to be more accurately determined by navigators at sea
than was then possible; and it was with the object of obtaining
pecuniary assistance to assist him in completing his chronometer that
Harrison had, in 1728, made his first visit to London to exhibit his
drawings.

The Act of Parliament offering this superb reward was passed in 1714,
fourteen years before, but no attempt had been made to claim it. It
was right that England, then rapidly advancing to the first position as
a commercial nation, should make every effort to render navigation less
hazardous. Before correct chronometers were invented, or good lunar
tables were prepared,[7] the ship, when fairly at sea, out of sight of
land, and battling with the winds and tides, was in a measure lost. No
method existed for accurately ascertaining the longitude. The ship
might be out of its course for one or two hundred miles, for anything
that the navigator knew; and only the wreck of his ship on some unknown
coast told of the mistake that he had made in his reckoning.

It may here be mentioned that it was comparatively easy to determine
the latitude of a ship at sea every day when the sun was visible. The
latitude--that is, the distance of any spot from the equator and the
pole--might be found by a simple observation with the sextant. The
altitude of the sun at noon is found, and by a short calculation the
position of the ship can be ascertained.

The sextant, which is the instrument universally used at sea, was
gradually evolved from similar instruments used from the earliest
times. The object of this instrument has always been to find the
angular distance between two bodies--that is to say, the angle
contained by two straight lines, drawn from those bodies to meet in the
observer's eye. The simplest instrument of this kind may be well
represented by a pair of compasses. If the hinge is held to the eye,
one leg pointed to the distant horizon, and the other leg pointed to
the sun, the position of the two legs will show the angular distance of
the sun from the horizon at the moment of observation.

Until the end o