[ 33i ] 
u the high land of Sanda Martha, 7 0 45' E. nearly 
“ fouth of Port Royal : Therefore thefe curves are 
tc not much altered 3 and the curve at Jamaica is 
“ nearly at a ftand, as tho’ tied ; and the fouth part 
“ of them, with the reft, dropping to the weftward.” 
Mr. Mungo Murray, author of a treatife on fhip- 
building, prefented us with feveral obfervations taken 
on board the Prince Edward and Chefterfteld Eaft 
Indiamen, and his Majefty’s fhip the Neptune. 
For all thefe favours we return our ftncere thanks. 
No obfervations made upon land have been re- 
ceived, except Dr. Bradley’s aforefaid 5 which has 
fruftrated our intentions of continuing the curves 
from fea to fea. 
By colleding, comparing, and adjufting, all thefe 
materials, we have been enabled to conftrud varia- 
tion-curves upon Dr. Halley’s mercator-chart, ad- 
apted to the year 1 7 56 3 which will foon be in rea- 
dinefs to prefent to this Royal Society. 
As a work of this kind requires much time, and 
a multitude of obfervations, both by fea and land, to 
render it more perfed and general 3 we hope the in- 
genious in all nations will lend their aftiftance : By 
this means every periodic review will be productive 
of improvement. 
From the firft inftant that we made this affair the 
object of our more particular confideration, we have 
attended to the mode of increafe and decreafe in the 
variation: and as a confiderable number of obferva- 
tions, made at periodic times, and duly regiftred, 
feem to be the moft eftential toward determining the 
laws of its mutation, or proving its irregularity, we 
have therefore formed a fett of tables, from actual ob- 
fervations collected for the years 1710, 1720, 1730, 
and 1 744, the date of our laft chart 3 which, together 
U u 2 with 
