Royal Society. 227 
arlfingfrom the magnetic variation, and change of the bearing 
of lines, may be avoided. Tho' a furvey may be taken truly 
without magnetic initruments, fo as to ihew the exa6l angles, 
and lines of the plat, and confequently the true contents 5 yet 
this will not give the true bearings of the lines, or fhew, for 
inftance, my pofition in refpe^t of my neighbours, or other 
parrs of the country ^ this muft be fupplied by the magnet, or 
Ibmething equivalent.thereto, as finding a true meridian line 
on your land by celeftial obfervations ; and Mr. Molyneux 
doubts not, but the ancient Egyptians^ before the difcovery of 
the magnet, were forced to fome fuch expedient in their liir- 
veys, and applorments of land, after the inundations of the 
Nikj which, we are told, gave the firft rife to geometry and 
furveying ; and this leads to another objedlion, which may be 
made againft the inftance before laid down j it may be laid, 
that the furveyor, which B employed, was very ignorant, who 
would chufe to judge of the line PQ^ rather by its bearing, 
than by determining the point Q^ by meafure from H to G. 
To this it is anfwered, what if both the points H and G were 
vanifhed fince the furvey was taken 5 what if the whole face of 
the country were changed, fave only the point P, and the line 
VQj, how fhall the furveyor then judge of the line PQ^, but 
by its bearing? That this is no extravagant fuppofition, we 
have an example in Bgypt^ where the iV//e lays all flat before 
it, and fo uniformly covers all with mud, that there is no 
diftinftion 5 in fuch a cafe, your bearing muft certainly help 
you out, there is no other way. But, fecondly, to fay that the 
furveyor might have determined the point Q_by admeafurement 
from G to H, or any other adjoining noted points, as from 
F, K, I, ^c. is very true, but then it is againft our fuppofition; 
we are now fliewing an error, that arifes from judging of the 
line PCi. by magnetic bearing, and to lay that this might be 
avoided by another way, is to fay nothing; it has been /hewn 
already, how it may be avoided, 'viz. by allowing for the 
variation, but ftill it is an error till it is avoided. But, thirdly, 
if B's furveyor do not allow for the variation of the needle, 
he will never exasflly determine even the points G, F, H, K, 
^)C. or any other points in the plat, but inftead thereof, he 
will fall on the points ^, ^, /, k. 
From what has been faid, we may fee the abfolute neceflity 
of allowing for the variation of the magnet, in comparing old 
furveys with new ones; for want of which, great difputes may 
arife between neighbouring proprietors of lands 5 and it were 
F f 2 #> te 
