318 Daniell on n )iew Hi/gromeler. 



the varying elements of the compound air we breathe. The 

 eudiometric processes which were immediatelv instituted and 

 repeated in every part of the world, proved, however, the unvary- 

 ing proportions of the permanent gases of which it is composed. 

 May we not indulge an expectation, that an accurate method of 

 estimating the varying quantity of aqueous vapour in the elastic 

 medium which surrounds us, which is the only fluctuating ingre- 

 dient of its composition, may lead to some useful hints upon 

 this important subject ? Certain it is, that some indications of 

 this kind may be perceived, even by the healthy, and those who 

 are not conversant with the progress of disease. There are days 

 when even the most robust feel oppression and languor, which 

 are commonly and justly attributed to the weather ; while, on 

 others, they experience exhilaration of spirits, and an accession of 

 muscnlar energy. Some such days I have endeavoured to mark 

 in the journal of observations. 



The 3d of September was particularly oppressive, close, and 

 relaxing. The temperature of the air was 68°, and the hygrome- 

 ter marked the point of condensation at 65°, indicating upwards 

 of 64 grains of vapour in the cubic foot. Evaporation was next 

 to nothing. Rain eusued, and the atmosphere was relieved. 

 On the 6th of September, the temperature of the air was within 

 2° as high as on the 3d, but the point of condensation was 20° 

 below, and the quantity of vapour in the cubic foot was very 

 little more than 3^ grs. The day was fresh and exhilarating. 

 On the 7th, the quantity had again increased to nearly its 

 former point, accompanied by the same effect upon the feelings. 

 On the 20th of November, there was very little more than 

 two grains of vapour in a cubic foot of the air. The atmos- 

 pheric temperature was 35°, but the cold was very cutting, and 

 very much beyond what was indicated by the thermometer, on 

 account of the great dryness which prevailed. The oppression 

 of sultry days may be accounted for, from the obstruction of 

 the insensible perspiration of the body, which is prevented 

 from exhaling into the atmosphere, already surcharged with 

 moisture ; while unimpeded transpiration from the pores, when 

 the air is more free from aqueous vapour, adds new energy to 



