XI. On the Motion o/" L i g h t, as affeEied by refraEling and 

 refleBing Subjlances, 'which are alfo in Motion. By JOHN. 

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

 Philofophy in the Univerjity 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 ; and there is none 

 from whofe writings 1 have received fuch variety of inflrudlion 

 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 diftindlly the progrefs of his own 

 mind in his refearches. 



Mr Boscovich has lately obliged the public with a colledlion 

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

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

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

 the aberration of light, or the effedl which is produced on the 

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



/a There 



