PREFACE 



TO THE FIRST EDITION. 



THE want of a popular treatife of philofophy, one 

 which might ferve as a proper introduction td 

 natural hiftory ; to explain to general readers the. great 

 principles and operations of nature; to give, in a 

 united view, the discoveries of the moderns on thefe 

 , important fubjedts, firft fuggefted to me the prefent 

 undertaking. 



It is now many years fince I projefted this work; 

 and I intended to have termed- it, "The Phiiofoph/ 

 of Natural Hiftory." In that title I have been antir 

 cipated ; but my plan, though long fince announced 

 very amply to the public, has not yet been anticipated, 

 and the work is Hill as much wanted as when I firit 

 conceived the intention of undertaking it. 



To diftinguifh certainty from conjecture is the mofl 

 difficult tafk of the fcholar ; a tafk which few find lei- 

 fure, fortitude, or attention to complete. In the pre- 

 fent imperfect (late of knowledge, when I fay certainty , 

 I perhaps would confine the refearches of human, wildom 

 within too narrow limits; and probability *mny be the: 

 more fuitable expreflion, which muft, indeed, compre- 

 hend no inconfide rable portion of our difcoveries in 

 nature. To feparate, therefore, the probable from the 

 fanciful, was my firft object j and, if I was not appre- 

 henfive of being thought too alluming, I would add, 

 the ujeful from the fpeculative. I have obferved, that 

 in all fciences the principal difficulties arife from cer- 

 tain controverted and difputable points, which are of 

 little importance in themfelvcs, and which, as they are 

 not eltabliflied upon competent evidence, are not eafy 

 to be comprehended. 



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