353. 1st. Step. First, write down the Observation made on the Ground, or at the Bottom of the Mountain, thus:
Below. Barometer, 29 Inches 4 Tenths. attached Thermometer, 50 Degrees. Air Thermometer, 45°.
354. 2d. Step. Secondly, write down the Observation made at the Top of the Mountain, or upper Station in the Atmosphere, thus:
Above. Barometer, 25 Inches, .19 Tenths. attached Thermometer, 46°. Air Thermometer, 291⁄2.
355. 3d Step. Subtract the colder attached Thermometer, from the other attached Thermometer, thus: 46 colder from 50 warmer, and there remains 4° warmer, viz. the Number of Degrees of Temperature to which the colder Barometer must be expanded, before it becomes equal in Temperature to the warmer Barometer: each Barometer being always supposed equal in Temperature with its attached Thermometer.
356. 4th Step. Give the colder Barometer the same Temperature with the warmer: or, which amounts to the same, give the colder Barometer that Expansion which is communicated by the Addition of 4 Degrees of Temperature.
Both Barometers will then have the same Temperature, or Expansion, viz. an Expansion equal to the warmer Barometer.
This is to be done by referring to the first Table, for the Application of which there are separate Instructions: see the Explanation of the first Table.[118]
