^S METHODS OF OBSERVING THE LONGITUDE AT SEA, 



The lunar me- The imperfedion of the lunar method is, that in confequence 

 ever fubjea to ^^ ^^^ weather, or the moon's not being above (he horizon, it 

 thofe intervals fometimes happens that the, neceflfary obfervations cannot be 

 moon^'" * ot b ^^^^" ^^^ many weeks. And thefe long intervals between one 

 feen. lunar obfervation and another, muft for ever happen from the 



fame caufes; and thofe caufes are fuch as no human art can 

 remove. 

 Inftances of the La Peroufe, in his voyage round the world, was at one 

 fiTquencro"ob- ^'""^ ^ ^ ^^y^ without taking a {ingle lunar obfervation ; but he 

 ftrvations by had, within that time, 20 obfervations by his time-keeper. 

 tiTOe-pieces. ^^ another time during the fame voyage, 24 days elapfed 

 without a lunar obfervation ; but he had 20 obfervations by 

 his time-keeper. Lord Hugh Seymour, in his voyage to the 

 Weft Indies in the year 1796, had been at fea near fix weeks 

 before the firft lunar obfervation was obtained, in which pe- 

 riod the longitude had been obtained 30 times by his time- 

 keepers. 

 Time-keepers I What has jufi: been mentioned fets time-keepers in a very 

 "r Iter'- °or favourable light, but it remains to inquire into their imperfec- 

 be negleaed in tions. 1. A time-keeper may flop. 2. It may alter in its rate 

 winding up; or ^f going. 3. It may not be wound up through forgetfulnefs. 

 accident. And, 4. It is liable to other accidents, even in the moft care- 



ful iiands. But thefe are defects which may be removed, and 

 a refult obtained, which will be more perfect than by any time- 

 keeper that has yet been made. 

 JMctliod of ob- The method which I have to mention muft be known to 

 tainiiig a more rf,any gentlemen, as I had the honour to lay it before the com- 

 pfi fea refult rt ■ , • ■ ^i 



from time-keep- mitTioners of longitude m the year 1783. The method, bow- 

 ers.; propofed ever, feeins either very little known, or not much attended 

 yliK^L ^ to. La Peroufe made no ufe of it in his voyage round the 

 world ; hence it may be fuppofed that it was unknown in 

 France at that time. Nor is it once mentioned by Mr. Wales 

 in his excellent treatife on the method of finding the longitude 

 at fea by time-keepers ; although he had " been pretty inti- 

 mate with the fubjed for near forty years"*'. 

 It confifts in The method which I have recommended depends upon a 



*^'^'"S th^ "><^an particular ufe of time-keepers as they are now conftru8ed. 



reluit of a num- ' ' ■' 



ber of machines. Although the beft time-keeper be too imperfect a machine to 



be depended upon for determining the longitude in long 



• Pnf:,ce to Wales on the longitude, p, 5, 

 3 voyages,. 



