By John Frederic Daniell, Esq. 3 

 gardens is rendered congenial to the luxurious productions 

 of more favoured regions, and flowers and fruits from the 

 confines of the tropics, flourishing in the open air, daily 

 prove the triumphs of knowledge and industry. 



For the complete understanding of the subject in all its 

 bearings, and to enable us to derive all the practical advan- 

 tages which such an understanding would certainly afford, 

 it would be necessary to have a full knowledge of the 

 peculiarities of the climate of every region of the earth, a 

 knowledge which we are very far from yet possessing ; but 

 to which, rapid advances are daily making. But above all, 

 it seems necessary that we should understand the atmos- 

 pheric variations of our own situation. These, though not 

 constituting the greatest range with which we are acquainted, 

 are great, and oftentimes sudden. The range of the ther- 

 mometer in the shade is from 0° to 90° of Fahrenheit's 

 scale ; but under favourable circumstances the heat of the 

 sun's rays reaches 135°, the changes of moisture extend from 

 1.000, or saturation, to .389 * Now the great object of the 



* The Dew-point (a term which will often occur in the course of this Paper) 

 is the degree of temperature at which the moisture of the atmosphere would begin 

 to precipitate, and may readily be ascertained at all seasons by means of the 

 hygrometer. The natural scale of the hygrometer is included between the points 

 of perfect dryness, and perfect moisture : the latter, of course, being that state of 

 the atmosphere at which the dew-point coincides with the temperature of the air. 

 The intermediate degrees may be ascertained by dividing the elasticity of vapour 

 at the temperature of the dew-point by the elasticity at the temperature of the 

 air : the quotient will express the proportion of moisture actually existing, to the 

 quantity which would be required for saturation ; for, calling the term of satura- 

 tion 1.000, as the elasticity of vapour at the temperature of the air is to the 

 elasticity of vapour at the temperature of the dew-point, so is the term ol satura- 

 tion to the actual degree of moisture. The necessary tables for facilitating this 



