Gases, consisting principally of light carburetted hydrogen or marsh gas, are of ten present in considerable quantity in coal, in a dissolved or occluded state, and the evolution of these upon exposure to the air, especially when a sudden diminution of atmospheric pressure takes place, constitutes one of the most formidable dangers that the coal miner has to encounter.
The south-westerly winds which prevail north of the equator during the hot half of the year, to which navigators have given the name of the south-west monsoon (the latter word being a corruption of the Indian name for season), arise from the great diminution of atmospheric pressure over Asia, which begins to be strongly marked with the great rise of temperature in April and May, and the simultaneous relatively higher pressure over the equator and the regions south of it.
This large quantity of air is forced through the furnace by means of the difference of pressure established between the external atmospheric pressure in the ash-pan and the pressure in the smoke-box.
In the north tropical belt of high pressure south of the Azores the atmospheric pressure in January is o 87 in.
Differences of temperature and atmospheric pressure must disturb this equilibrium, but the movements of both ocean and atmosphere lead to a high degree of uniformity in both envelopes as regards their gaseous constitutions.
Hot desert conditions are primarily found along the tropical belts of high atmospheric pressure in which the conditions of warmth and dryness are most fully realized, and on their equatorial sides, but the zonal arrangement is considerably modified in some regions by the monsoonal influence of elevated land.
Joule failed to observe any change of temperature in his apparatus, and was therefore justified in assuming that the increase of intrinsic energy of a gas in isothermal expansion was very small, and that the absorption of heat observed in a similar experiment in which the gas was allowed to do external work by expanding against the atmospheric pressure was equivalent to the external work done.
The following table contains the most probable values for a few of these points which have been determined with the greatest care or frequency: Table of Boiling-Points at Atmospheric Pressure on Centigrade Scale Alphabetical Index of Symbols Empirical constants in formulae; section 14.
The chief errors to which the stereometer is liable are (I) variation of temperature and atmospheric pressure during the experiment, and (2) the presence of moisture which disturbs Boyle's law.
Mead's treatise on The Power of the Sun and Moon over Human Bodies (1704), equally inspired by Newton's discoveries, was a premature attempt to assign the influence of atmospheric pressure and other cosmical causes in producing disease.