20 ON THE STUDY OF 



instrument of animal respiration, of vegetation, of 

 combustion, and of the different combinations 

 and changes which are constantly taking place 

 in nature: while its electric properties give rise 

 to the formation of lightning, clouds, snow, hail, 

 rain, meteors, and most of those atmospherical 

 phenomena which are more or less daily occurring 

 to our observation. Thus the doctrines of the 

 atmosphere branch out into various subjects 

 which of themselves may be considered so many 

 distinct sciences; for the illustration of which a 

 great many very important instruments have been 

 invented. -Among these, the barometer, the ther- 

 mometer, the eudiometer, the hygrometer, the air 

 pump, the electrical apparatus, and some inge- 

 nious chemical instruments are the most conspi- 

 cuous. The air or atmosphere, therefore, forms 

 a most essential part of natural history ; and 

 being of very comprehensive operation, a study of 

 its laws and properties becomes a matter of deep 

 interest and importance. 



We come next to the doctrine of water, the 

 science of which we have denominated hydrology. 

 The common properties of this element are fluidity, 

 gravity, transparency, and in its more simple 

 state, insipidity. Its chemical or constituent 

 parts are oxygen and hydrogen, united, as it 

 has been supposed, by the agency of the elec- 

 tric fluid; the oxygen bearing in a very consider- 

 able degree the largest proportion. The subjects 



