[ 8 7S ] 
Tlhe following Addrefs having been read to this 
Royal Society, the Prefident and Council of the 
fame , being defirous to encourage , as much as may 
be, an Undertaking Jo ufeful \ defre the feveral 
Members thereof and their learned and inge- 
nious Correjpondents , to communicate their Ob - 
Jervations , directed to their Secretaries^ in Crane- 
Court, Fleet-Street. 
CVII. An Attempt to point out , in a concife 
matmer , the Advantages which will accrue 
from a periodic Review of the V ariation of 
the magnetic Needle , throughout the known 
World ‘ y addrejfed to this Royal Society by 
William Mountaine a?td James Dodfon, 
Fellows of the faid Society , and requefting 
their Contribution thereto y by communicat- 
ing fuch Obfervations concerning /V, as they 
have lately madey or can procure fro?n their 
Correfpondents in foreign Parts . 
London, March 20, 1755. 
Read March 20, A BOUT the year 1700, the juftly 
* 755 - /\ celebrated Dodtor Edmund Halley 
having collected together a great number of obferva- 
tions, made on the variation of the needle, in many 
parts of the world, drew (on a mercator C hart) cer- 
tain lines, fhewing the quantity of that variation, in 
thofe parts of the world, over the reprefentation of 
which thofe lines were drawn ; but as the quantity 
f S 2 of 
