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SECTION VII. 

 Observation of Air and Water. 



. As we can know and contemplate the powers 

 with which nature works, only through the me- 

 dium of those substances in which they are mani- 

 fested, a considerable portion of that which would, 

 perhaps, with more propriety, come in under this 

 or some of the succeeding parts of the book, has 

 been already anticipated, and what remains to be 

 said may, in some instances, have the appearance of 

 repetition. But that is unavoidable ; for if we are 

 to view nature as it exists living nature, we must 

 view it in its connexion. There is no dissecting 

 till after death ; and then, the very finest anatomy 

 that can be practised gives us only disjointed mem- 

 bers. But the observer wishes to know nature 

 in its activity and life; and, therefore, there is 

 no possibility of noticing any one thing usefully 

 to him without a glance at collateral things. 



In the case of the great agencies of gravitation 

 and cohesion, and light and heat, and motion 

 and resistance, that is especially necessary, inas- 

 much as, apart from the subject in which their 

 effects are displayed, we have not the slightest 

 conception or means of knowing any one of these. 

 There is no weight, unless there is something 

 that is heavy, and has other properties besides 

 weight ; there can be no cohesion, unless there is 



