[ \97 ] 
horizontal Rim or Circumference of the Compafs- 
box, will give the magnetical Azimuth of the Sun 
or Star. 
N.B. All this may be perform'd by one Perfon, 
whereas the old Compafs requires feVeral 
to manage it, which alio makes it fubjed to 
many great Errors. 
How the Variation of the Needle is found by mean& 
of Magnetical Azimuth and Altitude thus obtain'd, 
is taught in every Treatife of Navigation, and we 
have no need to repeat thefe Rules in this Place. But 
as the Refolution of this Problem is fomewhattrouble- 
fome, and requires fuch a Knowledge of the Dodrine 
of the Sphere, as every Seaman has not attain'd, we 
fhall here exhibit an eafy Method of difeovering the 
Variation of the Compafs without any manner of Cal- 
culation, which cannot fail to render this Inftrument 
ftill more acceptable : To this End, 
ijf y Let the Magnetic Azimuth of the Sun (or any 
Star, when it is near the prime Vertical, and confider- 
ably elevated above the Horizon) be found according 
to the Diredions already given, before it arrive at the 
Meridian, and note well the Altitude, or let the Index 
remain fix'd at the fame Point on the Arch. 
idly y Find the Magnetic Azimuth of the Sun or 
Star in like manner as before, when it is exadly at the 
fame Degree of Altitude, after it has pafs'd the Meri- 
dian: And, 
3 dljy If thefe two Magnetical Azimuths are equal, 
the Needle has no Variation : If unequal, add them 
together, and half their Sum will be the true Azi- 
muth \ or fubtrad the lefs from the greater, and half 
the Difference will be the Variation required. The 
Cir- 
