1;)6 On Ihn lidronu'hii'al .MfaauremcHl of Heh^hh. [AiKi. 



out at p. 60, vol. X. Substituting^ these augmented temperatures 

 for those obaervtd, v.e proceed in our calculations precisely the 

 siuiue us for dry air. VVhen we coaie to the explanation of the 

 tables, the method will be more fully described. 



But what are the equations when the observer has been 

 unfurnished with a hygrometer? Laplace has found on inves* 

 ligation of the observations of Ramond, that the correction for 

 humidity in the mean state of the atmosphere may be made 

 (without regard to pressure) by adding to the mean of the 

 detached thermometers half the equation for saturated air sup- 

 porting at that mean temperature a pressure of 30 inches.* 



The degree of saturation of a section of the atmosphere may 

 vary from several causes. It will be greater, ca^teris panbus, in 

 a maritime than an inland situation ; and in the midst of moun- 

 tains, especially if marshy, than when surrounding an arid peak 

 isolated in a level district. When the temperature is low, the 

 probability of the air being more nearly saturated is increased, 

 particularly if the wind should be from a quarter where the 

 (Quantity of vapour, from the proximity of the sea and the supe- 

 nor temperature, should naturally be considerable. We are also 

 led to infer from the experiments made in different latitudes 

 with the hygrometer of Mr. Daniell, that the correction for 

 humidity should be greater at the same temperature for eleva- 

 tions above the sea not exceeding 5000 feet than for extraordi- 

 nary altitudes. 



Guided by these remarks, when the observer conceives the 

 atmosphere to be unusually damp, let him add to the mean 

 temperature two-thirds of the equations given in the table at 

 p. 50, vol. X. On the other hand, when the air is judged to be 

 in a state of extraordinary dryness, he may consider the degree 

 of humidity as equal to one-third of the maximum quantity, and 

 make his corrections in conformity. 



( To be contimced.) 



* The formula of Laplace is incorrect for temperatures a little bdow (P C. The 



augmentation of the dilatation of dry air j — ) to — ^ in order to cover the increase 



•^ \'x?67/ 250 

 of humidity at elevated temperatures beyond its mean quantity at 0° (introduced in the 

 general coefficient) has the effect of making moist air at low temperatures appear more 

 dense than dry air. 



