( 4 l & ) 
puting each Knot at 50 Feet, the Circumference was 
6000 Feet, which I take to be the Standard of an 
Englijh Maritime Mile, or the Part of a Degree 
upon the Equator j in running which Length, my 
Inftrument has juft 6co Revolutions; to which Di- 
ftance a little Bell ftrikes to give Notice, to the Man 
at the Helm; of the Diftance failed in that Time. 
Belides the feveral Circles on this Dial (graduated 
as I have mentioned) I had alfo two Plates on each 
Side, having two Circles j one divided into ico 
Leagues, and the other into 300 Miles } fo that, with- 
out hearing the Bell ftrike to every Mile or League, 
one might at any Time fee by them, what Number of 
Miles or Leagues the Ship had run, from the Time 
(he had left her Port. 
As to the Materials within the Dial, there is little 
more than common Clock-work. 
As by this Machine I undertake to correft the Er- 
rors of the Log, I flatter my felf that a Comparifon 
between that Inftrument, and my Invention, will not 
be unacceptable to the Curious, I therefore prefent 
you with 
A Comparative Difcourfe between the Log and my 
Inftrument , which 1 chufe to call the Marine 
Surveyor. 
1 ft. ur pHE flrft Error I chufe to touch on, in re- 
<c X lation to the Log , is in the half and quar- 
cC ter Minute Glalfes • I think I may well affirm, that 
tc they are feldom or never true, in regard it rarely 
“ happens that we can find two to finilh their Courfe 
“ in the fame Space of Time ; yet, if they did run 
“ their Sand out equally, it is no Demonftration of 
<c their Truth, fince two, that are falfe, may do the 
“ fame 
