CHAPTER XV. 
METEOROLOGICAL REPORT—BY A. DE C. SOWERBY. 
METEOROLOGICAL observations were commenced at T’ai-yiian Fu, in 
Shansi, on May 16th, 1g08, and were kept up—with as much care and 
regularity as circumstances would permit—throughout the whole duration of 
the expedition, 7.e., till September 12th, 1909. The instruments used were :— 
One portable mercurial barometer. 
Three aneroid barometers. 
One hypsometer, with spare thermometer. 
One small psychrometer (wet and dry bulb thermometers). 
Three swing psychrometers. 
Six swing thermometers. 
One maximum and one minimum thermometer. 
One six-inch diameter rain gauge. 
All thermometers were graduated on the Fahrenheit system, while the 
barometers, boiling point thermometers, and swing thermometers were 
provided with Kew certificates. 
The barometer observations were made either with the mercurial 
barometer or with an aneroid. In the former case the readings have been 
corrected for temperature, so that they represent the true air pressure at 
station level; and in the latter case, comparisons between the mercury 
barometer and the aneroids were carried out at intervals, in order to guard 
against errors due to changes of zero in the aneroids. 
The readings of dry and wet bulbs printed in the diary were made with 
swing thermometers. This was necessary on account of the inevitable absence 
of a suitable screen for the exposure of the instruments. The reduction of 
the readings in order to determine the humidity of the air will therefore 
require tables appropriate to the well-ventilated psychrometer. The tables 
commonly used in England, which are based on Glaisher’s Factors, are not 
suitable for the reductions, and would give values of the relative humidity 
lower than the true values. The tables of the U.S. Weather Bureau, which 
were prepared for use with sling psychrometers, are more appropriate. 
The readings of the maximum and minimum thermometers are probably 
less reliable than those of the dry and wet bulbs, because it was necessary to 
improvise some shelter for them, and some of the readings may be affected by 
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