4T 3 Major-General Roy's Account of the 



of that number were ufed in any one ftatlon. They are of 

 clean deal, iipwarid's "^'^ five feet in length, one inch fquare, 

 and pointed with plate iron at the botton:, fo as to be eafily fixed 

 into the ground. Each rod carries a crofs vane, fix or fevea 

 inches in length, and three-quarters of an inch in breadth. 

 This crofs vane, being moved upwards or downwards along 

 the rod, till its upper furface coincided with the crofs wires of 

 the telefcope and black line on the painted board, its under fur- 

 face then marked the height to which the furface of the ftand 

 was to be brought at that particular place. In this manner, a 

 certain number of points, in the line paffing through the air 

 from one fixed ftand to the other, being accurately obtained, 

 it was very eafy, at all the intermediate places, by the appli- 

 cation of the eye alone to the furface of any one fland or rod, 

 to bring the furfaces of the other, flands near it into the fame 

 . plane. 



'Clip and T'ripod for preferring the 'point upon the ground, where 

 the meafurement was difcont'mued at nighty and refumed next 

 morning. Tab. XVIII. 



It has been already mentioned, and, in giving the account 

 of the rough meafurement with the chain, there will be far- 

 ther occafion to remark, that the bafe was divided into hypo- 

 thenufes of 200 yards or 600 feet each, where fquare pickets 

 were driven into the ground, and regularly numbered, fo as to 

 be eafily referred to on any occafion. In the meafurement 

 with the rods, it was cuftomary to finifh the day's work at or 

 near one of thefe ftations. When the rods of twenty feet 

 iwere ufed, the termination of a rod was, of courfe, always 



found 



