X PREFACE* 



jtime, afforded of doing justice to those eminent per* 

 sons who have preceded him in this branch of in- 

 quiry. To those also who feel a pleasure in tracing 

 the progress of the mind through the details of an 

 extensive and complicated investigation, it may be 

 interesting to observe, in what a slow and successive 

 manner the knowledge which we at present possess 

 has been acquired : how many individuals, often at 

 very distant periods, have been employed in adding 

 to it : and how many observations, apparently, at 

 first, trivial and insulated, have, in the progress of 

 science, assumed an unexpected importance, serving 

 to connect together a long series of facts, which, but 

 for such casual aid, might still have remained dis- 

 jointed and broken. Reflections such as these, 

 while they encourage every one to contribute his 

 share, however small, to the general stock of know- 

 ledge, may, at the same time, serve to abate some- 

 what of that unpardonable vanity which has led some 

 philosophers to assume the sole merit of having 

 raised the edifice, when, in fact, the foundation was 

 entirely laid by others, and they themselves have on- 

 ly assisted in arranging and giving form to the ma- 

 terials of which the superstructure may hereafter be 

 composed. 



Without entering into formal and minute descrip- 

 tion, it has been a principal object through the 



