a 8 MifceUanea Curiofa. 



ing of Iron Mines and Loadftones in the Earth) 

 put a ftop to all further Contemplation ; and 

 give difcouragement to thofe that would other- 

 wife undertake this Enquiry. J Tis true, that not 

 long fince one Mr. Bond, an old Teacher of Na- 

 vigation, put forth a fmall Treatife, wherein he 

 pretends to calculate the Variation : But he li- 

 mits his Hypothecs to the City of London, affir- 

 ming himfelf (as he had a great deal of reafon) 

 that the lame Calculus is not fufficient for other 

 Places ; whereby it appears that this Rule is far 

 fhort of the fb much defir d general one. 



Now although (through want of fufficient Ob- 

 fervations, and fome other Difficulties, which I 

 fhall anon (hew) I cannot pretend perfectly to 

 eftablilh the Numbers and Rules of a Calculus, 

 which (hall precifely anfwer to the Variations of 

 all parts of the World : Yet I fuppofe it will not 

 be unacceptable to the Curious to propofe fome • 

 thing of a Light into this abftrufe Myftery ; 

 which, if no other, may have this good Effect, 

 to ftir up the Philofophical Genii of the Age to 

 apply themfelves more attentively to this ufeful 

 Speculation. But before I proceed, 'twill be ne- 

 cefTary to lay down the Grounds upon which I 

 raife my Conclufions ; and at once to give a Sy- 

 nopfis of thofe Variations, which I have reafon to 

 look upon as fare, being moftly the Obfervations 

 ©f Perfons of good Skill and Integrity, 



A 



