TO THE 



RIGHT HONOURABLE 

 THE PRESIDENT, 

 VICE-PRESIDENTS, 



AND 



MEMBERS OF THE SOCIETY 



FOR THE 



ENCOURAGEMENT OF ARTS, 



MANUFACTURES AND 



COMMERCE. 



THE Extenfion of every Branch 

 of ufeful Knowledge being the great 

 Objeft of the SOCIETY for the Encou- 

 ragement of ARTS, MANUFACTURES 

 and COMMERCE, the Author begs 

 Leave to commit the following 

 Treatife to their Patronage. 



London, March 26th, 1779. 



