XI. On the Motion o/Light, as affe died by ref racing and 

 reflecling SubJIances, -which are alfo in Motion. By fOHR 

 Rob I SON, M. A. F. R. S. Edin. and Prof effor of Natural 

 Philofophy in the Univerfity of Edinburgh. 



[Read by Mr PlaTFAIR, April 7. 1788.] 



FE W of the mathematicians and philofophers of the pre- 

 fent age have acquired a greater or better founded repu- 

 tation than the celebrated Abbe Boscovich j and there is none 

 from whofe writings I have received fuch variety of inftruction 

 and entertainment. His Theory of Natural Philofophy will 

 ever be confidered by impartial judges, not only as one of the 

 boldeft, but alfo as one of the moft ingenious refearches into 

 the fecrets of nature. There is hardly a branch of phyfico- 

 mathematical philofophy which he has not cultivated with fuc- 

 cefs ; and in this cultivation he has exhibited the moft acute pe- 

 netration and the greateft addrefs. In all his inveftigations too 

 he has given the moft beautiful fpecimens of geometrical in- 

 vention and elegance, and greatly heightens the pleafure of his 

 readers, by marking out diftinctly the progrefs of his own 

 mind in his refearches. 



Mr Boscovich has lately obliged the public with a collection 

 of feveral of his fmaller works in five volumes quarto, publifh- 

 ed at BafTano in 1785. In the fecond and fourth volumes of 

 this collection, are two very curious papers, on what is called 

 the aberration of light, or the effect which is produced on ;the 

 apparent place of vifible objects by the motion of the obferver. 



/ 2 There 



