Note 41 — Chapter III

This expression is not strictly correct, as it was impossible to maintain absolutely the same level throughout without using stools of an unmanageable height. What was done was to keep the rods in a right line until a new gradient was designedly taken; the angle of rise or fall being in each instance carefully measured, and the whole afterwards reduced by computation to the exact horizontal distance. It may be added, that in order to make due allowance for the elongation or contraction of the rods by change of temperature, thermometers were attached to the apparatus, and the rise and fall of the mercury duly recorded.