ADVERTISEMENT. Vll 



The Third Volume is intended to contain 

 the Principles of Optics, together with those 

 of Electricity and Magnetism. This will 

 complete a work which lays claim to no 

 other merit, but the very humble one of 

 expressing elementary truths in a distinct 

 manner, and placing them in a right order. 



EDINBURGH COLLEGE, 

 October 1814. 



NOTE. 



Sept. 27. 1819. 



This Edition is printed from a copy prepared for the 

 Press by the Author. EDITOR. 



CONTENTS 



