IN OPTICS. oy 



circumference of a circle; and hence some 

 very different figure would be observed. Every 

 person, however, may easily convince himself, 

 that the circular form of the fiery appearance 

 is equally perceived, whether the eye be at rest, 

 or be moved in the most irregular manner. 



If these arguments be thought sufficient for 

 the purpose I had in view, it must also follow 

 from them, since the fact still remains to be ex- 

 plained, why we apparently see so many objects 

 with equal distinctness at once, that past im- 

 pressions upon the retina are perceived as pre- 

 sent, by means of some higher faculty than that 

 of sight. This faculty cannot, with propriety, 

 be named memory y as it is essential to a thing's 

 being remembered, that it be perceived #s past. 

 Nor can it be called imagination, since we be- 

 lieve in the present existence of what it per- 

 ceives. In one point of view it may seem 

 rather a defect in our natures, that we should 

 not be able to distinguish between things past 

 and present. However this may be, I am in- 

 clined to be of opinion, that many other pheno- 

 mena, both of thought and external sense, are 

 partly to be resolved into the same general fact. 

 From the present instance of it, we learn, that 

 several muscular actions may be performed, in 

 succession, during the least perceptible portion 

 of time. 



