A. D. 1762. ^^^ 



the fhip's rate of going between the flated times of heaving the log, &c. 

 Hence a method of afceitaining the longitude, with the fame degree of 

 accuracy which is attainable in the latitude, has for ages been the 

 grand defideratum in navigation: and fince the year 1714, when the 

 parliament offered a reward of _^20,ooo for the bell method of afcer- 

 taining the longitude at fea, many fchemes have been devifed, but all 

 to little or no purpofe, as going generally upon wrong principles, till 

 that heaven-taught artift, Mr. John Harrifon, arofe. 



It is evident, that as the globe revolves round its axis in twenty-four 

 hours, every one ot the 360 degrees of longitude mufl: be equal to four 

 minutes of time ; and coni'cquently, that if a (liip has failed from any 

 given point, where the fun was in the zenith, (or in his meridional al- 

 titudej and next day, when the fun is in the zenith, it is found by a 

 watch, which goes perfedly true, that it is four minutes after twelve, 

 the fhip has made one degree of difference of longitude to the weft- 

 ward ; or, if the watch wants four minutes of twelve, one degree of 

 eaft longitude ; and To in proportion for any greater or lefs difference. 

 Hence nothing more is required to make us fure of the longitude than 

 a watch perfedly true. But watches, like all other productions of hu- 

 man art, are liable to error, and are, moreover, in a confiderable de- 

 gree affedled by the changes of the atmofphere. To the correction of 

 thefe defeds Mr. Harrifon devoted the adiduous ftudies of a long life ; 

 and he produced, what is probably, in principle, the neareft approach 

 that ever will be made by human ingenuity to the great objed of the 

 wifhes of navigators and philofophers, a chronometer or time-keeper, 

 which, in tvvo voyages made by his fon to the Weft-Indies, under the 

 diredion of the commiftioners of the longitude, was found to determine 

 the longitude at fea with an accuracy beyond the niceft exadnefs re- 

 quired by the ad of parliament, as appeared by certificates from the 

 captain and officers of the Ihip, which was appointed to attend him on 

 the trial, and alfo from the governor of Jamaica. 



The board of longitude thereupon paid Mr. Harrifon ^ic^oo. And, 

 that we may conned the whole of this bufinefs together, parliament 

 next year ordered ^,'5000 to be paid to him, on condition that he fliould 

 lay open to the public the principles upon which his time-keeper was 

 conftruded : and they promifed to pay him the remainder of the 

 /^20,ooo, if on farther trials in the courfe of four years it ftiould ftill 

 be found to afcerlain the longitude within the required limits of exad- 

 nefs ; during which time no other artift ftiould be permitted to compete 

 with him in the fame line of difcovery. \^/lcl 3 Geo. Ill, c. 14, fxiffed 

 317? ALircb 1763.] At diffi-rent times thereafter Mr. Harrifon obtained 

 payment of the remainder of the ^^20,000. 



Time-keepers have ever fmce been made upon Mr. Harrifon's prin- 



Y y 2 



