g2 



APPENDIX, 

 reckoning, in whatever degree it takes place, ahead of 

 the fhip. 



By obferving M. Bouguer's rules in comparing it with 

 the common log, which for that purpofe mull be reck- 

 oned at fifty-one feet, it will, I think, very fully corred 

 the third and fourth, which are the moft material errors; 

 as the agitation of the fea from winds does not exceed the 

 depth to which the diver is let down, and the weight of 

 the whole machme prevents the fridion of the reel from 

 having an efFe£t in any degree equal to that which it has 

 on the common log. 



The fifth arifes from the imperfedion it has in common 

 with the log generally ufed. 



At fir{}, on the paflage out, 1 contented myfelf with 

 heaving Bouguer's log occafionally, to obferve what pre- 

 cautions were neceflary to be taken to prevent errors, as 

 well as to find whether its variations from the common 

 log were on the fame fide as the meridian obfervation 

 required. I found that it was neceflary to take care that 

 the diver {hould be of fuch a weight as to let only the 

 top of the cone fwim ; but not heavy enough to fink it, 

 as in that cafe it would be liable to an error in excefs, by 

 meafuring the depth that the diver would fink in addition 

 to the ihip's way. It was neceflTary to put a weight of 

 lead to the bottom of the diver, to fink it down to its 



pake 



