1054 Transactions of the American Institute. 



quentlj tlieir precision of time-keeping was not such as to attract the 

 attention of astronomers and artists to any great extent. Hiiyghens 

 of Holland soon made the very important discovery that the long and 

 short vibrations were not made in precisely equal times, and he 

 invented the cycloidal checks, which secured perfect isochronism but 

 were not practical. 



Wm. Clement, of London, soon after invented the steel pendulum 

 spring, to take the place of the thread or cord hitherto used for sus- 

 pension. This spring, when made of the proper thickness, had all 

 the advantages of the cycloidal checks, but took afraetion more power. 

 In 16S0 Clement brought out the Anclior, or what is usually termed 

 the Recoil Escapement, which allowed of a much longer, heavier 

 pendulum, and a much less arc of vibration. This invention posses- 

 sed great merit, and Clement seemed fairlj^ on the road to fame and 

 fortune, when, all at once, it occurred to Dr. Hooke that he had 

 invented that escapement twenty years before. The distinguished 

 philosopher Huyghens also invented the retaining power ; a number 

 of minor improvements were made by others about this time, but the 

 great and crowning achievement of all was the invention of the dead 

 beat pallet and the mercurial pendulum by Geo. Graham about 1T15 

 to 1720, in which the expansion of the rod is compensated by the 

 expansion of mercury in the opposite direction. The Gridiron 

 pendulum was invented by Harrison about 1726. It keeps the rod 

 of the same length by the expansion of solid metals in opposite direc- 

 tions, but, bringing the center of oscillation too high and always 

 operating by jerks, the Gridiron pendulum can never be made so 

 reliable as that pendulum carrying a cylinder cap of mercury. It 

 will thus be seen that all of the great principles applied in time- 

 keeping have been used for 150 years, or more. 



England seems to have fostered and nurtured the art of horology, 

 which is so important to navigators of the sea, but it seems not to 

 have been indigenous to the brain of that country. I have men- 

 tioned that Dutch clockmakers were invited to come in and ply their 

 trade ; and Frenchmen and Germans nmst have been invited, or came 

 without, for I find that at the commencement of the seventeenth cen- 

 tury there were fifteen clock and two watchmakers in London, and 

 every one of them loas a foreigner. They had, too, a spice of what 

 Sam Slick would call " human nature " about them, for the moment 

 they got settled in London they commenced clamoring for protection 

 from foreign makers. They asked this favor from James I, and 



