Miscellanea Curiofa. a 87 



to the fuppofal of any other Variations at 

 the firft and fecond Surveys, Mutatis mu- 

 tandis, for knowing the Variations we know 

 their Difference ; and if we know their Dif- 

 ference, this gives us the Angle QJ? by 

 which we reduce them to each other. 



The belt way therefore to make Maps in- 

 variable, conftant and everlafting , were for 

 the Surveyors , who ufe Megnetick Inftru- 

 ments to make always allowance for the 

 Magnetick Variation, and to protraft and 

 lay dbwn their Plats by the true Meridian. 

 This the wary Sailer is fully convinced of : 

 and therefore in Steering his Courfe, he con- 

 ftantly allows for the prefent Variation, which 

 he obferves T)y the ~Axkyuth Compafs, or elfe 

 he would mifs his appointed Harbour oftner 

 then he would hit it : For ho two Points on 

 the Globe keep the fame Bearing to each 

 other by the Magnetick MeVidian for any 

 time together. And though the Variation 

 be flow, yet in a long Courfe , or in times 

 pretty diiiant, it may caufe vaft Errors, un- 

 lefs allowed for. Thus for inftance , fup- 

 pofe in the year 1660. a Sailor had fteered 

 from the Land's end of England to Gape Fini- 

 fter in Spain 1 by his Magnetick Compafs 

 a direct South Courfe *, and that at that time 

 there were no Variation. Afterwards Anno 

 1700. when there was (fuppofe) 7 Degrees 

 of Variation from the North to the Weft- 

 ward, another Sailor intending to make the 

 fame Palfage, fleers direclly the fame South- 

 erly Courfe by his Magnetick Compafs : I fay, 

 this laft Seaman will be carried far into the 

 Bay of Bifcay to the Eaftward, and will mifs 



of 



