Seer. III. i. MOTIONS OF THE RETINA. 17 



To render this circumftance more eafy to be com- 

 prehend e 1 motion may be defined to be a variation of 

 fgure ; for the whole univerfe may be confidered ag 

 one rhino; pofTeffmg a certain figure ; the motions of 

 any of its parts are a variation of this figure of the 

 whole : this definition of motion will be further ex- 

 plained in Section XIV. 2. 2. on the production of 

 ideas. 



Now the motions of an"organ of fenfe are a fuc- 

 cefllon of configurations of that organ ; thefe con- 

 figurations fucceed each other quicker or flower ; 

 and whatever configuration of this organ of fenfe, 

 that is, whatever portion of the motion of it is, or 

 has ufually been, attended to, conftitutes an idea* 

 Hence the configuration is not to be confidered as 

 an effect of the motion of the organ, but rather as 

 apart or temporary termination of it; and that, 

 whether a paufe fucceeds it, or a configuration im- 

 mediately takes place. Thus when a fucceffion of 

 moving objects are prefented to our view, the ideas 

 of trumpets, horns, lords and ladies, trains and 

 canopies, are configurations, that is, parts or links 

 of the fuccellive motions of the organ of vifion. 



Thefe motions or configurations of the organs of 

 fenfe differ from the fenforial motions to be defcrib- 

 ed hereafter, as they appear to be (imply contrac- 

 tions of the fibrous extremities of thofe organs, and 

 in that refpect exactly referable the motions or con* 

 tractions of the larger mufcles, as appears from the 

 following experiment. Place a circular piece of red 

 filk about an inch in diameter on a (heet of white 

 paper in a ftrong light, as in Plate I. look for a 

 minute on this area, or till the eye becomes fome- 

 what fatigued, and then, gently clofing your eyes, 

 and (hading them with your hand, a circular green 

 area of the fame apparent diameter becomes vifible 

 in the clofed eye. This green area is the colour 

 reverfe to the red area, which had been previoufly 

 C 2 infpected, 



