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TO THE SECOND EDITION 



THE former edition of this little work was given to 

 the public in the shape of Lectures, as delivered, in 

 compliance with the regulations of the Chair which 

 the author then occupied, and without any expecta- 

 tion that its use would extend much beyond the circle 

 of his immediate hearers. It has however found its 

 way elsewhere ; and the author has been urged, by 

 some of his fellow-labourers in other Universities, to 

 reprint it. With this request he could not but com- 

 ply ; and he trusts that the delay in acceding to it 

 may be excused to those who made it, by the desire 

 of the author to render the work more deserving of 

 their favourable estimation. 



In the present edition some account is given of 

 the more important discoveries in Physical Optics, 

 which have been made since the publication of the 

 former. In preparing these additions, the author 

 has derived much aid from the Repertoire d'Optique 

 Moderne of the Abbe Moigno 3 a work which contains 



