309 



sure in proportion to the mean pressure at great altitudes than near the earth's 

 surface. Referring bo the Meteorological Statistics of the Colony, an abstract 

 of which is given at the end of Transactions of the New Zealand Institute, 

 Vol. ii., on "The Climate of IvTew Zealand," it will be seen that the height of 

 Bealey Station, above the sea-level, is 2100 feet, and the barometrical range 

 for 1869 is 1-132 inches, while the mean annual range at the other stations 

 in the South Island is 1 -4 ', and it will be found by dividing the mean 

 observed pressure by the mean range, that the fluctuations of pressure are less 

 at great altitudes. Complete observations at different altitudes near the same 

 station are, however, yet wanting, which would throw light upon the manner 

 in which the variations of pressure are communicated from lower to upi:)er 

 regions and vice versa. It is known also that the air is subject to different 

 horizontal motions at different altitudes at the same time, where it would only 

 be in a column of air which is perfectly stationary that the barometer at the 

 bottom would give the absolute weight thereof at any given instant. That the 

 barometer informs lis of changes and expected changes of weather is generally 

 conceded ; superior pressure indicating fine weathei', and low pressure the 

 reverse. But what is the nature of the connection ] When aqueous vapour 

 is added to a given weight or column of dry air, that column must be so much 

 heavier, why should not therefore the barometer rise 1 



Again, when the temperature of the air rises, which it often does before 

 and during storms, why does not that increase of temperature keep the watery 

 vapour in it from precipitating as rain 1 Again, chemists have succeeded in 

 liquefying many gases by su.bjecting them to pressure. When, therefore, the 

 atmospheric pressure increases, why should not its aqueous vapour (if at its 

 point of maximum density) be precipitated as rainfall ? With reference to the 

 first question, when watery vapour is taken up into the air, why should not 

 the barometer rise ? It must be I'emembered that heat has accompanied the 

 moisture in its evaporation, which leads to the expansion of the column 

 beginning at the bottom ; it is therefore a moving column upwards, in which 

 case its absolute weight could not be given by the barometer, but only its 

 pressure at the given instant. 



It has been shown by Dov^, that the warm moist air of the equatorial 

 regions is in an expanded state, and would flow in the higher regions towards 

 the poles; and since the equatorial regions of the earth revolve about 1000 

 miles per hour, while at the poles the motion is at the minimum, it follows 

 that the currents of equatorial air in southing have a tendency to keep their 

 easterly motion, and thus form a wind, which, in this latitude, would come 

 from a north-westerly direction, often at a considerable height ; whereas the 

 cold polar curi-ents, being continually left behind while passing towards the 

 equator near the earth's surface, would reach us as a dry, cold, south-easterly 

 wind. 



