HimaAtava Mounrarns, 297 
indeed I had laid it down, that if I could obtain a degree of accuracy, volitol 
would leave not more than an uncertainty of one foot in 5000, it would be as 
much as [ could hope for, and sufficient to ensure all the advantages, for the 
attamment of which the measurement was undertaken, 
3. Tur next point was to settle in what manner the rods were to be 
constructed. ‘Uh’s was cf course, ta depend a good deal on the nature of 
the stands which could be obtained. General Roy’s rods were twenty feet 
in length, and trussed vertically, and laterally to prevent bending —pieces 
of ivory, with fine hives drawn on them, being inserted in the extremities for 
the purpose of making the contact perfect. The method of contacts was- 
however found’to. consume toc much time, and. metal buttons projecting: from 
the ends of the rods—were made to butt against each other. In using" rods: 
of this description, heavy stands with elevating: screws were indispensible: 
These'I have already noticed were out of the question, and therefore this. 
mode: of construction was necessarily abandoned.. Foreseeing from the 
first, the great time that it would. cost to prepare stands of any description, 
Thad contemplated the possibility of doing without them,, and in the follow= 
ing manner:—Supposing a number of stout pickets driven into. the ground 
at distances of twenty-five feet, I thought a vod of this length; well trussed, 
and furnished with points, forming in some measure a ‘large beam-com- 
pass, might be used for setting off accurately this length from picket to: 
picket. This method would have been sufficiently expeditious, and would. 
have required hardly any apparatus; but on mature consideration I feared 
it would be attended with more error than is allowable. ‘The measure- 
ment being, conducted so near the ground would have occasioned great 
VOL. XIV.. 3M 
