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Art. XVII .— On the Influence of the Hygrometric State of 
the Atmosphere upon the Minimum Temperature of the 
Night. By Adam Anderson, M. A. F. R. S. E., Rector 
of the Academy of Perth. 
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A. HE connection between the minimum temperature of the 
night, and the contemporaneous state of the air, in regard to hu- 
midity^ was first pointed out, I believe, in the Article Hygro- 
metry, which 1 wrote several years ago for the Edinburgh 
Encyclopaedia. In that dissertation I remarked, that, as the 
temperature of every place for the whole year ranges between 
two extreme points, corresponding to the alternations of sum- 
mer and winter ; so it exhibits, during the diurnal rotation of 
the Earth upon its axis, a like difference resulting from the vi- 
cissitudes of day and night. In the case of the daily change of 
temperature, there is some interval between the maximum and 
the minimum condition, which may be regarded as the tempe- 
rature belonging to the season of the year ; and though that 
point is not, at all times, equally distant from the extremes be- 
tween which it oscillates, it seldom departs far from their mean. 
If this mean temperature were to rise and sink regularly, as 
the year advanced and declined, without being subject to daily 
fluctuation, the quantity of moisture existing in the atmosphere, 
at any given time, might be determined by the thermometer 
alone, with considerable precision ; as it would generally be less 
than the quantity corresponding to the mean temperature, and 
seldom greater than that which belongs to the minimum tempe- 
rature, the latter setting limits to the accumulation of watery 
vapour in the atmosphere, while the former no less effectually 
secures it against a state of long continued dryness. The truth 
of these assertions will be readily perceived, by a comparison 
of the minimum temperature with the point of deposition, or 
the temperature at which the moisture existing in the atmo- 
sphere would begin to deposite itself. I shall select for this pur- 
pose the observations which my friend the Rev. Dr Gordon made 
in the year 1815, during his residence at Kinfauns ; not only be- 
cause they were made without any view to the support of a 
VOL. XI. NO. 21. JULY 1824. 
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