of the Variation of the Compass at Jamaica. 351 
on the new diagrams from recent surveys made by the mag^ 
netical needle, of the same original marked lines on earth, 
preserved as before described ) ; so that whatever course is 
laid down for the line on the diagram annexed to the patent, 
(and let it be supposed, for example, to be north and south, 
or east and west,) upon setting the compass in the old marked 
line on earth, and directing the sights north and south, or 
east and west, according to the magnetical needle, the said 
marked line on earth, originally run by the magnetical needle 
130 or 14,0 years ago, has been found by me to be exactly in 
the line, or direction with that of the compass ; consequently 
no alteration of the variation could have taken place during 
the whole, or any part, of that period of time in Jamaica. 
To this it may not be unacceptable to subjoin a short 
history of the practice of surveying in Jamaica, from the 
Restoration to the present time, in order to obviate any doubt 
that might arise, whether there be not a possibility of the 
quantity of the magnetical variation having been ascertained, 
and allowed for, in the first diagrams annexed to patents ; 
and whether the variation of 6\ degrees east, which corres- 
ponds with the magnetical needle now, might not then, have 
have agreed with the true meridian. 
The variation of the compass was first observed by Columbus, 
in his first voyage across the Atlantic, in the year 1492 ; and 
seemed to threaten that the laws of nature were altered in an 
unknown ocean. It is evident, however, that Columbus was 
not able to ascertain the quantity of variation ; for if he had 
ascertained it, the danger he was in would have been dimi- 
nished, if not entirely removed. His discovery, therefore, 
must have been, simply, the deflection of the magnetical 
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