1825.] Variation of the Mariner^ s Compass, ^^%| 



5. Sine 1. ..'^i'^\f/^' 9-65362 ' "^^ - ^-^"^ fir.;^^:..., 



6. Sine 2 9-30750 



19-38631 ^^ . - ' ; : -^^ 

 8. T. ^-^1^ ...,/.. 9-73269 == 28° p3^^^ W 



Thevefore / M . . ♦ ♦ . Xi'c^i. . . . = 81 07 58 



,..j ^L ♦*H.f. - 24 21 42. i 



fii Was observed in August. *•;.;•= 24 21 10 ^^ 

 ^j, DijBference ,*...• *j4(iw « 4> 5«r (^r^p [■^■f^^uma^ 



SineS.... 9-67706 ' ^' ''^' ' ^ ^- "' ^ loi^^Jf ^ 



Sine 4.... 9-90089 .v ^ fMod 



T. 2 9-31664 ' 



T. 5L&t^,^,^.54047 = 19^ 08^ 33'^pompleinenfcofdip. ^ 



_jj.: =.70 51 27 ' "*_. .^ r 



MM'ir-=:o38^^..17 .06^ ''^ ^ -m'^my-i ' 



How Mttcli^^fee-tKp was by observation, I dd not ^now ; but to 

 judge by that of 1812, this cannot be far from the trutli, because 

 it must necessarily have increased since. ^^ ' 



^ According to the series of observations placed S0^e end, 

 with which I have been favoured lately by some gentlemen of 

 the Royal Society, it appears that the variation had attained the 

 highest degree in 1814, and that it has been gradually dimi- 

 nishing from that time. This diminution, however, is not a 

 sufficient proof of the actual return of the needle towards the 

 north : for I find, from a number of observations made by Dr. 

 Gilpin, that a much greater diminution had taken place in an 

 equal space of time to that from 1814 to 1824, after which the 

 variation was found to increase again; liamel;^, in 1800 it was 

 observed 24° 36' W. and in 1809 it was found by thie same 

 gentleman 24° 11'; that is, 25 minutes less; after which it 

 appears to have continued to increase until 1814, when it 

 amounted to 24° 21' 10", and has retrograded smce, in the 

 space often years, to 24° 9' 33", which is only lF37"less than 

 the greatest of 1814. If, therefore^ 25' diminution in nine years 

 did not confirm the return of the needle towards the north, much 

 less can 11' 37" diminution in 10 years confirm such a return; 

 and the question must as yet remain undecided. I have further 

 to observe that the ^ M in the last example, being le^s than 

 90°, supposing the data correct, is an evident proof that the 

 variation had not then attained its highest degree, which can 

 only take place when that angle is 90°, which, according to the 

 last given annual progress, will be in the year 1829, when the 



