4 <3 Major-General Roy’s Account of the 
of that number were ufed in any one ftation. They are of 
clean deal, upwards of five feet in length, one inch fquare, 
and pointed with plate iron at the bottom, fo as to be eafily fixed 
into the ground. Each rod carries a crofs vane, fix or feven. 
inches in length, and three-quarters of an inch in breadth. 
Th is 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 Hand 
was to be brought at that particular place. In this manner, a 
certain number of points, in the line palling through the air 
from one fixed Hand 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 Hand or rod, 
to bring the furfaces of the other Hands near it into the fame 
•plane. 
Cup and fripod for preferring the point upon the ground , where 
the meafurement was difcontinued at night , 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 wms cuftomary to finifh the day’s work at or 
near one of thefe ffations. When the rods of twenty feet 
weremfed, the termination of a rod was, of courfe, always 
found 
