VI PEEFAOE. 



My chief object has been to bring proininently 

 forward those facts which appear to me to be 

 supported by earperimental evidence, and of paramount 

 importance ; the apphcation of these facts must be a 

 subject for future consideration. 



I may observe, in conclusion, that whatever suc- 

 cess may have attended my labours, I cannot lay claim 

 to any originality ; for I shall have the pleasure of 

 shewing, that our predecessors, with all our boasted 

 advantages of superior means of investigation, enter- 

 tained very correct notions upon the subject. They 

 pursued and exhausted the subject as far as they 

 could, and then threw out conjectures for others 

 to verify. 



Cambbldqe, 

 September, 1860. 



