Note A — PART II. CHIEFLY SCIENTIFIC. (continued 2)

Great care is necessary on the part of the man who measures the displacements. The staff ought to be placed along the original line, and the assistant ought to walk along it until the foot of a perpendicular from the stake is attained. When several days' motion is to be measured, this precaution is absolutely necessary; the eye being liable to be grossly deceived in guessing the direction of a perpendicular.