( i^o6 ) 
III A Letter of Dr Wallis to Capt/iin Edmund 
Hallcy } concerning the Captains Map of Mag- 
netick Variations h and fome other things rc^ 
lating to the Magnet. 
Oxfordy May 7^. 1702. 
sir; 
f Scnt you a Letter about three weeks fince, ( v/hicb, I 
hope you received, ) with my hearty Thanks for the 
Prefent you had then fent me 5 your Map of the M^gm^ 
tick, Variations. 
I look upon the thing as an Excellent Defign, and very 
Inftrudive 5 well Contrived, and well Executed 5 And 
which, I think, was never undertaken by any, before 
For a true Natural Bifiory of matter of Faft, is certain* 
ly the fureft Foundation on which to ground a Phyfical 
Hypothejisy to explain t\\Q Caufes. r ; 
1 am very well pleafed to fee, upon the whole, ^ fo pro- 
mifing a Profpeft, as (to me) this feems to be. 
It fixcth the bufinefs of Magnetick Variation (in thefe 
Seas) for the Prefent Time. If like Obfervations had been 
•made in former Ages, and tranfmitted to us, it would 
have been of great ufe^ But it is now too late to wiQi 
for that. . 
It like Obfervations (hall be made for the Future, from 
time to time, and Recorded 5 whereby it may ^appear, at 
what Rate the Variation Varies 5 it will afford . a great 
In-light into the Magnetick Dodrine, of which we are fo 
much in the dark. 
I hope 
