CHAPTERLXX.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 providea Barometer, (whose Bulb or Cistern islargeenough to contain all the Quicksilver in the Tube;)—into the Frame of which, a Thermometer, onFarenheit’sScale, is to be fixed orattached.The Use of theattached Thermometeris to point out the Temperature of the Barometer.2d. A second ordetached Thermometeris 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 thegeneralTemperature of the Air at the same Time and Place: and may be called theAir Thermometer.A proper Person, on the Ground, having a good Watch, with Pen Ink and Paper at Hand, is to attend the Instrumentsbelowevery ten Minutes, (or at any otherpreconcertedIntervals 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 theattachedThermometer.4th, and lastly, the Degree of Temperature of thedetachedorAir-Thermometer.This Employment is to be carefully attended to; during the Time, thatsimilarObservations, bypreconcertedAgreement, are making, with three othersimilarInstruments, on the Top of the Mountain, or any elevated Station in the Atmosphere,by Means of theBalloon; and to be written with ared LeadPencil, in a Patent Asses Skin Pocket Book.The Instruments to be compared on Return from the Mountain, or upper Station.Each single Observation, made with one Set of Instrumentsbelow, is to be compared with each single corresponding Observation, made with the other Setabove.And two Observations are said tocorrespond, when both are madenearlyat thesameTime, the onebelow, and the otherabove.351. Take Shuckburgh’s first Example, (Ph. Tr. for 1777, 2d Part, Page 577.) viz.“Let the Point at which the Quicksilver stands in the Barometer, on the Ground, be 29 Inches 4 tenths: the attached Thermometer 50 Degrees of Temperature, and the Air Thermometer, or general Temperature of the Air 45°: at the same Time, that at the Top of the Mountain, or other elevated Station in the Atmosphere, the Barometer stands at 25 Inches 19 Tenths, the attached Thermometer at 46°, and the Air Thermometer at 39° and 1⁄2: required the upper Height in English Feet.”Rules for the Work: and Practice of the first Example.352. The Work is divided into three Stages.The End proposed in this first Stage is to bring the colder Barometer, to the sameExpansionorTemperaturewith theother.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 Observationmade 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 thecolder attachedThermometer, 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 thecolderBarometer must beexpanded, before it becomes equal in Temperature to thewarmerBarometer: each Barometer being always supposedequalin Temperature with itsattachedThermometer.356. 4th Step. Give thecolderBarometer the sameTemperaturewith the warmer: or, which amounts to the same, give thecolderBarometer thatExpansionwhich is communicated by the Addition of 4 Degrees of Temperature.Both Barometers will then have the sameTemperature, orExpansion, 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]
CHAPTERLXX.
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 providea Barometer, (whose Bulb or Cistern islargeenough to contain all the Quicksilver in the Tube;)—into the Frame of which, a Thermometer, onFarenheit’sScale, is to be fixed orattached.
The Use of theattached Thermometeris to point out the Temperature of the Barometer.
2d. A second ordetached Thermometeris 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 thegeneralTemperature of the Air at the same Time and Place: and may be called theAir Thermometer.
A proper Person, on the Ground, having a good Watch, with Pen Ink and Paper at Hand, is to attend the Instrumentsbelowevery ten Minutes, (or at any otherpreconcertedIntervals 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 theattachedThermometer.
4th, and lastly, the Degree of Temperature of thedetachedorAir-Thermometer.
This Employment is to be carefully attended to; during the Time, thatsimilarObservations, bypreconcertedAgreement, are making, with three othersimilarInstruments, on the Top of the Mountain, or any elevated Station in the Atmosphere,by Means of theBalloon; and to be written with ared LeadPencil, in a Patent Asses Skin Pocket Book.
The Instruments to be compared on Return from the Mountain, or upper Station.
Each single Observation, made with one Set of Instrumentsbelow, is to be compared with each single corresponding Observation, made with the other Setabove.
And two Observations are said tocorrespond, when both are madenearlyat thesameTime, the onebelow, and the otherabove.
351. Take Shuckburgh’s first Example, (Ph. Tr. for 1777, 2d Part, Page 577.) viz.
“Let the Point at which the Quicksilver stands in the Barometer, on the Ground, be 29 Inches 4 tenths: the attached Thermometer 50 Degrees of Temperature, and the Air Thermometer, or general Temperature of the Air 45°: at the same Time, that at the Top of the Mountain, or other elevated Station in the Atmosphere, the Barometer stands at 25 Inches 19 Tenths, the attached Thermometer at 46°, and the Air Thermometer at 39° and 1⁄2: required the upper Height in English Feet.”
Rules for the Work: and Practice of the first Example.
352. The Work is divided into three Stages.
The End proposed in this first Stage is to bring the colder Barometer, to the sameExpansionorTemperaturewith theother.
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 Observationmade 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 thecolder attachedThermometer, 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 thecolderBarometer must beexpanded, before it becomes equal in Temperature to thewarmerBarometer: each Barometer being always supposedequalin Temperature with itsattachedThermometer.
356. 4th Step. Give thecolderBarometer the sameTemperaturewith the warmer: or, which amounts to the same, give thecolderBarometer thatExpansionwhich is communicated by the Addition of 4 Degrees of Temperature.
Both Barometers will then have the sameTemperature, orExpansion, 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]