4'is}. Mcijor-Gcneral Roy's Account of tloe 



of the ftem of the deal rods indifferently, but always at the fixed * 

 -or hindermoft end of the glafs rods, the brafs ruler was advanced 

 fo near as almofl to touch the wire, and there made faft. This 

 being done, the mahogany half-crofs was laftly moved back- 

 wards or forwards, in the diredion of the line of meafurement, 

 ■■until the interfe£lion, as feen by a perfon lying down on the 

 aground forthe purpofe, accurately coincided with the gilt wire, 

 where it was likewife faftened by its proper fcrews. A tent 

 was then pitched very near the apparatus, for the foldiers who 

 furniflied the centinel for its fecurity, till the meafurement 

 was refumed ; and particularly to guard it from being 

 •^iilurbed by cattle during the night. 



Wheels for ienn'matlng^ In a permanent manner^ the extremities of 



It he Bafe. Tab. XVIII. 



Before any accurate meafurement could ultimately be made 

 of the bafe by means of rods, in order that we might with 

 certainty refer to the fame poir^t, on any occafion that might 

 arife of correction or repetition of the work, it had all along 

 been forefeen, that it would be abfolutely neceffary to fink deep 

 into the ground wooden pipes, or fuch like things, at the ex- 

 tremities of the bafe, which could not be removed, or even 

 difturbed, by idle or ignorant people, without very confiderable 

 labour. Mr. Mylne, F.R.S. was accordingly requefted to 



* That this might be conveniently done, a moveable ftand was placed, under 



the glafs rod, about four feet from the fixed end, and its table elevated till, by 



bearing againft the lower part of the cafe, it received its weight. This permitted 



the ftand undei the fixed cad to be lowered and removed, to make room for the 



♦ apparatus. 



order 



