646 ADDITION. 



to circulate uniformly in a direction contrary t6 

 that, in which the obferver had revolved. 



M. Sauvage has, laftly, mentioned the theory of 

 colours left in the eye, which he has termed im- 

 preflions on the retina. He fays, " Experience 

 teaches us, that impreffions made on the retina by 

 a viiible object remain ibme feconds after the object 

 is removed ; as appears from the circle of fire which 

 we fee, when a fire-ftick is whirled round in the 

 dark; therefore when we are carried round our own 

 axis in a circle, we undergo a temp@rary vertigo,- 

 when we ftop ; becaufe the impreffions of the cir- 

 cumjacent objects remain for a time afterwards on 

 the retina." Nofolog. Method. Claf. VIII. I. i. We 

 have before obferved, that the changes of thefc 

 colours remaining in the eye, evinces them to be 

 motions of the fine terminations of the retina, and 

 not impreffions on it ; as impreffions on a paflive 

 fubftance muft either remain, or ceafe intirely. See 

 an additional note at the end of the fecond volume, 



Dura, Liber ! aftra petis volitans trepidantibtrs alls, 

 Irruis imniemori, parvula gutta, mari. 



Me quoque, rne currente fota revolubilis setas 

 Volverit in tenebras, i, Liber, ipfe fequor. 



INDEX 



