THERMOTICS. ATMOLOGV. 519 



its collective form : but such knowledge is, in fact, 

 composed of parts of many different sciences. And 

 it is useful for our purpose to consider separately 

 those portions of Meteorology which have reference 

 to the laws of aqueous vapour, and these we may 

 include under the term Atmology. 



The instruments which have been invented for 

 the purpose of measuring the moisture of the air, 

 that is, the quantity of vapour which exists in it, 

 have been termed Hygrometers ; and the doctrines 

 on which these instruments depend, and to which 

 they lead, have been called Hygrometry ; but this 

 term has not been used in quite so extensive a 

 sense as that which we intend to affix to Atmology. 



In treating of Thermotics, we shall first describe 

 the earlier progress of men's views concerning Con- 

 duction, Radiation, and the like, and shall then 

 speak of the more recent corrections and exten- 

 sions, by which they have been brought nearer to 

 theoretical generality. 



