by foiiie general rule : yet T6 it is $■ that almoft all the Au- 
thors ^ from whomeadifcourre ofchis kind ought to have 
been expeded , pafs by in filence the difEcukies they here 
encoanten And thofe that mention this Variation ; by 
aliirming it to proceed ffom caufes altogether uncertain 
("as arethecaCial lying pf ^^pn mines and Loadfton es in 
in the Earth ) put a flop to ^11 further contemplation ; and 
give difcouragement to thofe that would otherwife under- 
take this Enquiry. Tis true that not long tfince one Mr. 
Bond^ an old Teacher of Navigation, put forthafmall 
Treatife wherein he pretends to caiculate the Variation r 
but he limits his Hypothefis to the City of London ^ [afErm- 
ing hinifelf (as he had a great deal of reafon^ ) that the fame 
Calculus lis not fufficient for other places ^ whereby it ap» 
pears that his rule is far fhort ofthe fomuch defired gene- 
ral one. : ' ■■ 
Now altho fthrough Want of fdfFicient obfervations and 
fome other difficulties which I (hall anon ffiewj I cannot 
pretend perfe£bly to eftablifli the numbers and rules of a 
Calculus which fliall precifely anfwer to the Variations of all 
parts of the World ; yet f fuppofe it v^rill not be unaccepta* 
ble to the curious to propofe fomething of a light into 
this abftrufe myftery ; which, if no other* may have this 
good efFed , to ftir up the Philofophical Genij oftfie age 
to apply themfelYes more attentively to this ufefar ^ctr* 
lation. But before I procceed 'twili beneGej[Iaryto:lay 
down the ga^r ^dl upon v^hich iraiMmy:Cpncluiions r atK^ 
at once toglv iyj^oplis of thofe Variations which I have 
reafbn : oli upon as fiire , Being moftly the dbler^raicF 
. ^^.P^i'f -'^iis of good-feiJl and Integrity. ■ - " 
