Clocks with the balances above de scribed, imperfect as they were, gave,. however, some assistance to astronomy. Tycho Brahe had four of them, but of such a massy construction, that a single wheel in one of them,which had but three wheels, contained 1200 teeth, and was three feet in diameter. These clocks continued in use till about 1650, when a new era in the art commenced, by the application of the pendulum as a re gulator.
Bernard, one of the professors of as tronomy at Oxford, in the last century, has asserted that the Arabians used pen dulums in . astronomy long before the above period, (as we know that Ricoli, Tycho Brahe, Langrenus, Vendelin, Mersenne, Kircher, Hevelius, Mouton, and Galileo himself did,) in a detached state ; but we do not find that any of them used it in conjunction with wheel work. According to professor Venturi, Sancto rius applied a pendulum to clock-work some time before the year 1625; and Becker mentions a native of Switzerland, called Juste Birge, who did the same in 1597 ; but these experiments, if really never were sufficiently made pub lic to benefit the world.
The person to whom mankind is real ly indebted, for bringing this important discovery into universal notice, is the celebrated Christian Huygens, of Zuy lichem, who, in his excellent treatise De Horologio Oscillatorio," has de scribed the construction of a pendulum clock, and proved that he made one be• fore the year 1658.
Galileo is supposed to have claims to the priority of the invention of the mode of applying the pendulum to clock-work, and his son Vincentio Galilei is reported (Expel. del Acad. del Cimento) to have made a pendulum clock so early as in 1649, at Venice, suggested by his father's discoveries. But it is thought that flay gens' method was much more masterly and scientific ; and that the world is not under any obligation to Galileo for the invention ; for, if he really made it, the manner of performing it was kept so se cret, that Huygens himself never heard of it, though one of the most philosophi cal characters of his time. There has another claimant appeared of late years for the honour of the invention, on the authority of Mr. Thomas Grignon, of Rus sel-street, Covent Garden, who produces a well authenticated writing of his fa ther's, to prove his having seen the in scription on the great clock, formerly fixed in the turret of St. Paul's, Covent Garden, which ascertained that it was made by Richard Harris, of London, in 1641. This clock was regulated by a long pendulum ; and, if the above infor mation is correct, must have been one of the first made, as it precedes that said to have been constructed by Vincentio Ga lilei by eight years. Mr. Grignon senior
was a very ingenious mechanist, and a man of excellent character, and brought to perfection the horizontal principle in watches, and the dead beat in clocks„ which the celebrated Tompion and Gra ham were unable to effect. These cir cumstances render his testimony of con siderable weight.
Huygens must, however, still be con sidered as the chief introducer of the in vention, which no one disputes having been made by him, even though others may be supposed to have made it like wise, unknown to him. He also invented a clock with a centrifugal regulator, which is contrived to pertbrm its move ment in a curve that he has demonstrat ed will render its gyrations isochronal, and which, at least, is worthy of a farther investigation, before it be condemned to an oblivion that it probably does not me rit. But his discovery of the isochronism of all vibrations made by a pendulum formed to move in a cycloidal curve is that which is the most noted, although it has never yet been really applied to use. Mr. Huygens' method of doing so has been shown clearly to be erroneous, by Mr. Alexander Cummings, in his " Trea tise on Clock and Watch Making," pub lished in 1766, whohas also asserted that the cycloidal principle would not be of the benefit imagined, "as the inequality of the vibrations of the pendulum moving in a circular arc correct those caused by the alteration of its weight from the va riations of atmospherical gravity, so as mutually to balance each other, while in those moving in cycloidal curves there is no principle to counteract the varia tions of gravity." It must, however, be noticed, that Mr. Cummings is evidently not correct in his statement, that the loss of specific gravity in the pendulum, caused by an increase in the weight of the atmosphere, would equally tend to prolong its vibrations, as the increased resistance caused to its motion by the same means would tend to diminish them, as he has by no means proved the equality of those opposite effects. Mr. Cummings also mistakes the loss of rela tive gravity for the loss of real gravity ; the momentum of a body in motion is ge nerally considered to be the same in dif ferent mediums, except so far as the ad ditional resistance from a denser medium retards it, and so far from Mr. Cum ming's opinion in opposition to this be ing as evident as he supposes, it is well known that no proof has ever been ad vanced to support it.