Xll PREFACE. 



pace with the advancement of this most 

 important discovery ; and though necessity 

 was the parent of the mechanic arts, yet 

 they also throve, and grew to maturity, 

 under the same influence. 



Many more instances might be added 

 to this brief view of the utility of natural 

 knowlege ; but we shall only give some 

 of its uses in the polite arts, which have 

 hitherto been too little connected with it. 



To instance particularly in painting, its 

 uses are very extensive : the permanency 

 of colors depends on the goodness of the 

 pigments ; but the various animal, vege- 

 table, and fossil substances (out of which 

 they are made), can only be known by 

 repeated trials ; yet the greatest artists 

 have failed in this respect : the shadows of 

 the divine Raphael have acquired an uni- 

 form blackness, which obscures the finest 

 productions of his pencil, while the paint- 

 ings of Holbein, Durer, and the Venetian- 

 school (who were admirably skilled in the 

 knowlege of pigments), still exist in their 

 primitive freshness. 



