The Particulars themfelves Follow •’ 
i. P o obferve th e Declinations andVt iriations of 
the Compajs or Jfeedle fromthe Meridian 
exactly , in as many Places as they can, and 
in the fame Places, every fever al Voyage. 
A T Ldn&> where by the help of good fixt Dials, and other fit 
Inftruments , the precife Meridian of the place may be 
known , it is eafie to find the Variation of the Needle ? divers 
wayes : As, by applying of the Needle , to the Shadow ofa 
Thred hanging perpendicular , when the'Sun is in th z Meridian* 
or to the Meridian Line 5 or the Side of a fixt Horizontal 
Dial , &c e 
But at Sea 3 in regard the Meridian is not fo eafie to be found to 
any tolerable exadnefs 5 to know the Variation of the Needle 3 is 
much more laborious and difficult. The Height of the Pole 0 and 
the Sms Declination being known , a large Ring- Dial , truly 
wrought , having a Box with a Compafs or Needle fixt to its Me- 
ridian below 3 may go as near as any other Inftrument , to fhew the 
Variation required. For, when it is fet to the juft hour and minute 
of the day , the Meridian of it ftands juft in its due place 5 and fo 
fhews how far the Needle varies from it 3 as exadly as the largenefs 
of the Card will permit. 
Eut becaufe thefe Dials are fo rarely juft 5 <^r. though they may 
be ufed and taken notice of, yet are they not to be relied on. The 
thing therefore is to be performed-, as followeth : 
Find out the S ms Azimuthal Difiance from the Meridian 3 fome 
hours before , or after Noon , and then its Magnetic al Azimuth^ 
or Diftaiice from the Meridian pointed at by the Needle 5 and the 
Difference of thefe two Diftances , is the Variation of the 
Needle. \ ! 
T o find the Suns tru sAzanmfh , or by how many Degrees 
oi tht Horizon Meridian : its Declination , its 
Altitude , and the Elevation of the Pole , muft all three be known. 
ills For 
