John Harrison received for his improved chronometers, in 1749, the Copley Medal; and, thus encouraged by the Royal Society, and by the hope of sharing the reward of 20,000l. offered by Parliament for the discovery of the longitude, Harrison produced in 1758 a time-keeper, which was sent for trial on a voyage to Jamaica. After 161 days, the error of the instrument was only one minute five seconds, and the maker received from the nation 5000l. For other chronometers, subjected, with perfect success, to a trial in a voyage to Barbadoes, Harrison received 10,000l. more. Dr. Stukeley writes of this ingenious man: “I passed by Mr. Harrison’s house at Barrow, that excellent genius of clock-making, who bids fair for the golden prize for the discovery of the longitude. I saw his famous clock last winter at Mr. George Graham’s: the sweetness of its motion, the contrivances to take off friction, to defeat the lengthening and shortening of the pendulum through heat and cold, and to prevent the disturbance of motion by that of the ship, cannot be sufficiently admired.”—Ms. Journal.[[18]]
An exact measure of time is of the utmost importance to many of the sciences. Horology is indispensable to astronomy, in which the variation even of two or three seconds is of the greatest consequence. By means of a clock the Danish astronomer, Roemer, was enabled to discover that the eclipses of Jupiter’s satellites took place a few seconds later than he had calculated, when the earth was in that part of its orbit the farthest from Jupiter. Speculating on the cause of this phenomenon, he calculated that light was not propagated instantaneously, but took time to reach us; and, from calculations founded on this theory, light has been discovered to dart through space with a velocity of about 192,000 miles in a second: thus, the light of the sun takes eight minutes to reach the earth.
Horology has also enabled us to discover that when the wind passes one mile per hour, it is scarcely perceptible; while at the rate of one hundred miles per hour it acquires sufficient force to tear up trees, and destroy the produce of the earth. And, without the aid of a seconds-clock, it would have been scarcely possible to ascertain that a cannon-ball flies at the rate of 600 feet in a second.
The use of Chronometers in geography and navigation is well known; since it is only necessary to ascertain the exact difference in time between two places, to determine their distance east or west of each other.
Graham applied the motion of a Clock showing sidereal time to make a telescope point in the direction of any particular star, even when before the horizon.
Alexander Cummins made a Clock for George III. which registered the height of the barometer during every day throughout the year. This was effected by a circular card, of about 2 feet in diameter, being made to turn round once in a year. The card was divided by radii lines into 365 divisions, the months and days of the month being marked round the edge, while the usual range of the barometer was indicated in inches and tenths by circular lines described from the centre. A pencil with a fine point pressed on the card by a spring, and, held by an upright rod floating on the mercury, faithfully marked the state of the barometer; the card, being carried forward by the clock, brought each day to the pencil. Wren proposed to have a clock constructed on a similar principle, to register the position and force of the wind; which idea has been adopted.
In the Armoury of George IV. was a model of a small cannon, with a clock attached to the lock in such a manner that the trigger could be discharged at any desired time by setting the clock as an alarum.
Breguet contrived a Clock to set a Watch to time. This clock is of the size of a chamber-clock, and has a fork and support on a top to carry the watch. When the clock strikes twelve, a piece of steel like a needle rises, and entering a hole in the rim of the watch-case, comes in contact with a piece which carries the minute-hand, and by pressure makes the hand of the watch correspond with that of the clock, provided the difference be not more than twenty minutes.
The same artist constructed for George IV. a Chronometer which had two pendulums, one making the machine show mean time, the other to make it act as a metronome by beating the time for music. This pendulum was merely a small ball attached to a slight chain carried round a pulley, on the centre of which was an index, which, when brought to any of the musical measures engraved on the scale, shortened or lengthened the chain, so as to cause the pendulum to perform its oscillations in the time required, and a hammer struck on a bell the beats contained in each bar; these would be silently struck by placing a piece of wood between the hammer and the bell; the musical time was also indicated by the seconds-hand of the clock.
A certain dynamical theory of chemistry has been propounded, founded upon precipitations and decompositions taking place in a definite space. Time forms, too, the very key by which alone we can be admitted to a proper view of the archives of the ancient world. Want of time for the due development of the geological periods, for a long season, hindered men’s conceptions upon this subject from taking a sharp, clear cast of thought. Linnæus constructed a Clock of Flora—a dial of flowers, each opening and shutting at an appointed time.[[19]]