242 



alteration has, for a considerable period, taken place there in the va- 

 riation of the compass. In that island all grants of land have a dia- 

 gram thereof annexed to the patent, wliich diagram is delineated 

 from an actual survey of the land to be granted, and has a meridional 

 line, according to the magnetical needle, laid down upon it ; but no 

 notice is taken of the true meridian. The boundary lines are marked 

 upon the land ; and in all disputes where the keeping up of these 

 lines has been neglected, surveyors are appointed to make actual re- 

 surveys, which are compared with those preserved in the secretary 

 of the island's office ; and it is expected that the lines and meridians 

 of the former will coincide with those of the latter. It is evident, 

 however, that this coincidence could not happen if any alteration in 

 the variation had taken place in the interval between the two sur- 

 veys. Mr. Robertson's business, as a surveyor, having been very ex- 

 tensive, he has had many opportunities of investigating the fact here 

 treated of ; and it appears from his observations, that the courses of 

 the lines and meridians delineated on diagrams annexed to patents 

 granted so long ago as the year 1 660, coincide with, and are parallel 

 to, the lines and meridians delineated on the re-surveys annexed to 

 deeds, &c., or on the new diagrams, from recent surveys made by 

 means of the magnetical needle, consequently no variation of the 

 needle could have taken place, in Jamaica, during the above period 

 of time. 



Our author subjoins to his paper a short history of the practice of 

 surveying in Jamaica, from the Restoration to the present time, in 

 order to obviate any doubt whether the quantity of the magnetical 

 variation was not ascertained and allowed for in the first diagrams 

 annexed to patents ; and whether the present variation of 6 degrees 

 east, might not then have agreed with the true meridian. He re- 

 marks, that until the year 1700, when Dr. Halley published his 

 theory of the variation of the compass, no observations to ascertain 

 the quantity of the variation in the West Indies had (so far as he 

 knows) been published ; and the variation at Jamaica, as laid down 

 by Dr. Halley, appears to have been the same as it is at present. Be- 

 sides, had the first surveyors allowed for the variation, in delineating 

 their diagrams, they would not have omitted to mention it ; and the 

 same system of surveying would have been continued, since a dif- 

 ference of 65 would have so totally deranged all boundaries, as to 

 have demanded legislative interference and correction. But no in- 

 stance of this kind has occurred. 



In the maps of the island made by the direction of Sir Henry 

 Moore, Governor (about the year 1760), the magnetic meridian only 

 is represented, although that gentleman was considered a great sur- 

 veyor. In short, the true meridian, our author says, has never been 

 noticed, nor the quantity of variation ascertained, nor the latitude or 

 longitude observed, by any surveyor or engineer in Jamaica except 

 himself. He has ascertained the variation to be 65 east, and has 

 assumed that as the true quantity, in the maps lately published by 

 him. 



