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magnetic attra&ions, in all probability occafioned by 
the heterogeneous competitions in the great magnet, 
the Earth. 
Notwithftanding all which, fhould the fagacity 
of fome eminent philofopher be able to exhibit rules, 
whereby the quantity of the variation may be com- 
puted for future times, yet then fuch a review, as 
we have now made, will be neceflary at a proper 
interval, to prove the truth of them : and fhould no 
fuch rules appear, then will a continued fuccetiion of 
fuch reviews be necetiary fo long as commerce and 
navigation fubtifl among us. 
What we have now done is intirely for the public 
fervice, the fale of the former chart never having 
made good its expence ; and we propofe to continue 
our endeavours for another review, at the proper 
time, if we fhall then be alive, and capable of the 
tafk : but as the contrary may probably happen, we 
beg leave to conclude with recommending fuch a 
continuation, in the ftrongeti: manner, to fuch of the 
members of this Royal Society, or others, who may, 
at the proper intervals, have leifure and ability for 
fuch a performance. 
We are, with the greateft deference. 
Your Lordfhip’s, 
And the Royal Society’s, 
Mod: faithful and 
moft obedient Servants, 
William Mountaine. 
James Dodfon. 
A 
