Chap. 36.] ttc Powers of Senfation limited. 367 



minated, and that we cannot determine at what point 

 of the circle the fire really is, and the fame circum- 

 flance may be obferved in the blending of colours, 

 which are yet marked diftinctly on a wheel before it is 

 turned. The evident caufe of thefe appearances is in 

 the eye ; and in the firft cafe, when we fix our eye on 

 any point of the circle made by the evolution of a 

 lighted coal, the illuminated object again returns to 

 that point before the fenfation previoufly produced is 

 worn off: and the blending of the colours on a wheel 

 is explained in the fame way ; for the impreffion made 

 by one colour remains till the other arrives and mixes 

 with it. It is alfo well known, that perfons who have 

 the beft and quickeft ears for mufic cannot judge ac- 

 curately of more than a certain number of notes in a 

 fecond of time. Innumerable fads, indeed, may ferve 

 to convince us, that the mind cannot well attend to two 

 or more fenfations at the fame time *. Hold your 

 tongue, faid a Frenchman, you talk fo I cannot tafte 

 my meat. The Frenchman was certainly right ; for 

 attention of mind is not lefs necefiary to full percep- 

 tion, than a healthy ftate of the organ of fenfe. 



All authors are agreed, that our knowledge of ex- 

 ternal objects is entirely acquired through the medium 

 of fenfation, though fome perfons of the higheft rank 

 in literature and philofophy ftill contend, againft Mr. 

 Locke, in favour of theexiftence of certain innate and 



* The contemptible vanity of Caefar, in pretending to perform 

 feveral mental operations at once, proceeded from a real igno- 

 rance of the human mind. The reply of the juftly celebrated 

 penfionary De Witt was much more judicious, and ought to be 

 imprefled on the mind of all young perfons. On being afked how 

 he contrived to tranfadt fuch a multiplicity of bufmefs in the courfe 

 of a day without negleft or difordcr, he anfwered, " I make it a 

 rule always to attend to one object at. a time." 



inftinctive 



