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]