METHODS TO ASCERTAIN THE TRUE HEIGHT.
Section 350.METHODS to be pursued on taking and comparing Heights, in order to ascertain the true Height of any Station in the Atmosphere, by the Barometer and Thermometers.
For this Purpose it is necessary, 1st, to provide a Barometer, (whose Bulb or Cistern is large enough to contain all the Quicksilver in the Tube;)—into the Frame of which, a Thermometer, on Farenheit’s Scale, is to be fixed or attached.
The Use of the attached Thermometer is to point out the Temperature of the Barometer.
2d. A second or detached Thermometer is also to be provided.[117]
This is to be hung in the Shade at the Distance of a Yard (or two) from the other:—to shew the general Temperature of the Air at the same Time and Place: and may be called the Air Thermometer.
A proper Person, on the Ground, having a good Watch, with Pen Ink and Paper at Hand, is to attend the Instruments below every ten Minutes, (or at any other preconcerted Intervals of Time,) putting down,
1st. The Time of each Observation.
2d. The Point at which the Quicksilver stands in the Barometer.
3d. The Degree of Temperature of the attached Thermometer.