ON THE MERIDIAN. u 



pleted, I placed the transit inftrument which is afed in laying out the 

 bafe lines, at a convenient diftance from one end of the wall, fuch that 

 the point of a fine pencil at the neareil end might "be dift'infily feerl 

 through the telefcope ; and by direding it to the other end, a few trials 

 enabled me co fee along the middle of the wall from one end to the 

 other.— After the indr^xnent had been well adjufted, a feries of points 

 was then made, about four feet from each other by looking through the 

 telefcope, anddire6ting a perfon with a fine pointed pencil in his hand, 

 to move it until it was brought into the interfedion of the wires in the 

 focus of the eye-^lafs; and in this manner the points were fixed from 

 one extremity of the wall to the other, and a pencil line drawn through 

 them. This being done, brafs fcrews with polifhed heads about 4^ 

 of an inch in diameter, were each ferewed fall into a fquare piece of 

 lead, leaving the brafs button about half an inch about it^ — The lead 

 was then funk into the chunam till the brafs coincided with the polifh- 

 ed furface of the wall, and adjufted by the longitudinal pencil line, and 

 others drawn at right angles to it at certain diftances roughly meafured 

 by the beam compaffes. Of thefe there were fourteen ; viz. five at 

 ■24 feet diftance, beginning with the neareft end, for the purpofe of 

 laying o^ ten feet from the brafs fcale ; and then one at every ten feet 

 from the laft one, to the compledon of the hundred.— All thefe being 

 fixed nearly correft, a fine line was drawn through the whole in the 

 direftion of the pencil line already mentioned ; on the firft of thefe 

 buttons, a crofs perpendicular line was drawn fo as to make an 

 interfeftion with the longitudinal one, and nearly in the center of 

 the brafs: this marked the commencement. Every thing being thus 

 prepared and the whole extent of wall ihaded by tents, the final mea- 

 furement was commenced at about the time of fun-rife, on the 24th 

 Marchf 1813, having it ftri6Uy in view to perform the whole opera- 



