386 



VAKTATION OF THE COMPAS*. 



said marked line on earthy originally run by the magnc- 

 tical needle 130 or 140 years ago, has been found by n»e 

 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. 

 Oil. Whether ^^ this it may not be unacceptable to subjoin a short 

 the variation history of the pracTtice of surveying in Jamaica, from the 

 imcient^tlmes" ^lestoration 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 an- 

 nexed to patefits : and whether the variation of 6| de- 

 grees east, which corresponds with the magni'tit-Al needle 

 now, might not then, have agreed with the true meridian. 

 The variation The variation of the compass was first observed by 

 Columbus ^ Columbus, in his first voyage across the Atlantic, in the 

 year 1492 ; and seemed to threaten that the laws of Na- 

 ture 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 diminished, if not en- 

 tirely removed. His discovery, therefore, must have been 

 simply the deflection of the magnetical needle from the 

 true meridian, without knowing the quantity thereof. 

 — and system- From this period down to the year 1700, when Dr. 

 atized by Hal- Halley published his "Theory of the Variation of the 

 1700 found the ^o™P^ss," no observations, ascqrtaining the quantity of 

 same variation variation, in the West Indies, were, I believe, published. 

 Dow"*^*^* ^^ ^® ^^^^ ^^® ^^^^ ^^'^^ made any in South America, and 

 these were chiefly applicable to the coast of Brasil. With 

 his theory was published " A new and correct Chart of 

 *' the whole World, shewing the Variations of the Com- 

 '' pass, &c. as they were found in 1700, by Direction of 

 '' Capt. Edm. Halley.'* By this chart the variation, at 

 Jamaica, appears to have been the same as it is at present. 

 His theory could have been known but to few ; nor do 

 any observations, in the West Indies, appear to have been 

 made for many years after its publication. Indeed I 

 know of none till very lately, and these only in a few 

 charts. But, however extensive its publicity might have 



been. 



