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Admiral Fitzroy&rsquos Words For The Scale
Admiral Fitzroy&rsquos Rain-gauge
Admiral Fitzroy&rsquos Scale Words
Aneroids
2 Construction Of Barometers
Causes Which May Bring About A Fall Or A Rise In The Barometer
Dial Or Wheel Barometers
Casella&rsquos Mercurial Minimum Thermometer
Causes Of Rain
Distribution And Effects Of Ozone

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Method Of Calculating Heights By The Barometer
Thermometric Substances
Varieties Of Thermometers
Mercurial Minima Thermometers Desirable
Thomson&rsquos Electrometer
The Common Formthe Barometer Is Of Great Use To The Mariner Who By Using It As A &ldquoweather Glass&rdquo Is Enabled To Fores
The Syphon Tube Mountain Barometer On Gay Lussac&rsquos Principle
Vacuum Solar Radiation Thermometer
Thermometers For Engineers
Mason&rsquos Hygrometer

Principle Of

If some mercury, or any other fluid, be poured into a tube of glass, bent in the form of ∪, and open at both ends, it will rise to the same height in both limbs, the tube being held vertically. If mercury be poured in first, and then water upon it at one end, these liquids will not come to the same level; the water will stand much higher than the mercury. If the height of the mercury, above the line of meeting of the fluids, be one inch, that of the water will be about thirteen-and-a-half inches. The explanation of this is, that the two columns balance each other. The pressure of the atmosphere in each limb is precisely similar; but the one column stands so much higher than the other, because the fluid of which it is composed is so much lighter, bulk for bulk, than the other. If one end of the tube be hermetically closed, the other limb be cut off within a few inches of the bend, and the tube carefully filled with mercury; by placing it in a vertical position, the mercury will fall, if the closed limb be long enough, until it is about thirty inches higher than that in the exposed limb, where it will remain. Here the atmosphere presses upon the short column; but not upon the long one. It is this pressure, therefore, which maintains the difference of level. In fact, it forms a barometer without a cistern, the short limb answering the purpose of a cistern. The first barometers on this principle were devised by the celebrated philosopher, Dr. Hook, as described in the next section.

Next: Dial Or Wheel Barometers
Previous: Use Of The Barometer In Estimating The Height Of Tides

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