Mechanical Philosophy, 69 



were brought to such a degree of accuracy as to 

 be thought worthy of a large premium from the 

 Board of Longitude, before mentioned. Mayer*s 

 tables were afterwards improved by Mr. Charles 

 Mason, of England, who reached a still greater 

 degree of precision in his calculations. And finally, 

 to the Rev. Dr. Maskelyne, the present Astro- 

 nomer Royal of Britain, is due the honour of 

 contributing much toward the perfection of the 

 plan, and of introducing it into general practice. 



Another method of finding the Longitude, by 

 observations on the Eclipses of Jupiter s moons ^ 

 though practised as early as 1688, has yet been 

 much improved during the period under discussion. 

 For these improvements, which are chiefly founded 

 on the superior extent and accuracy of modern ta- 

 bles, we are indebted principally to Drs. Bradley 

 and Pound, M. Cassini, the younger, Mr. War- 

 GENTiN, and M. Delambre, of whom the ta- 

 bles of the last have been generally adopted in 

 many of the late nautical almanacks. A third 

 mode of determining the Longitude, by well regu- 

 lated Time-keepers, is almost wholly a production 

 of the last age. For although some attempts of 

 the kind were made in the preceding century, 

 nothing effectual was done until 1714, when 

 Henry Sully, an Englishman, pubhshed a small 

 tract at Vienna, on the subject of watch-making, 

 and announced some improvements in the art, 

 with a view to the Longitude, which were said to 

 be valuable, and attended with success. This 

 plan, however, was afterv/ards brought much 

 nearer to perfection, by the ingenious and perse- 

 vering labours of John Harrison, also of England, 

 who, in 1726, produced a time-keeper of such un- 

 common accuracy as not to err above one second 

 in a month, for ten years together. Watches of a 

 similar kind, and which have proved of great uti- 



