358 ^ fdr* Wallan on [Oct. 



; to ^Hi3d eih io iioqc^ifh m - 



,,,, }:''r/W^)i^^f'#''^«i^: •■By Mr. J:waii^ 



-nnw [I i (To the E(Jitors of the Annals of Philosophpy lorft" 



yff 'j^.^JSlNTIfEMBN, , , Birmingham, SepUUA^h, 



The following appearances being quite new to myself, 1 coni- 

 municale them Tor insertion in the Amialsy that, !prQYJi,<)Q4 ,the 

 observations of others are found to correspond wit^tjipa^ o;wn, 

 they may be placed to their proper account. , 



The moon being aboijt 22 degrees above the western horizon, 

 having a small plano-convex lens in my hand, which was applied 

 close to my right eye, on looking at that body I perceived a faint 

 nebulous circle of light, and within the margin of this, and 

 almost on the right edge of it, a perfect image of the moon, 

 whose apparent size was somewhat less than the moon itself, 

 viewed with the naked eye. The light of this perfect image 

 was only so much greater than the circle, as to enable me to 

 distinguish it for a perfect picture of the planet. On applying 

 the glass to my left eye the effect was precisely the same, 

 except that the place of the perfect picture of the moon varied 

 a little in this instance from its situation in the former, being a 

 trifling degree nearer to the centre of the nebulous light. 



Although it might be deemed most prudent not to attempt at 

 accounting for this appearance until it had been more scruta- 

 nized, and the effect correctly verified by q, number of indivi- 

 duals, I cannot help concluding at once, from this slight dif* 

 ference in the observations made with each of my own eyes, 

 that the perfect picture was reflected from the base of the 

 optic nerve, and the circular image from the retina ; and I draw 

 this conclusion from a knowledge that there is a trifling varia- 

 tion in the axes of my own eyes, although not apparent to any 

 one except myself; as well as that there is in each a difference 

 in their capacity for distinct vision, — this being, in fact, more 

 or less the case with every one^ 



Having observed the same effect on several successive nights, 

 and during two sucessive lunations, it does not appear by any 

 means probable that there was the least illusion in this appear- 

 ance more than would take place with other spectators similarly 

 situated ; and the seat of vision being a point still under the 

 ban of dispute with philosophers, I make no apology for the 

 inference now drawn, but will zealously expunge it from my 

 <2atalogue of maxims, if the reverse can still be proved to be 

 troe by direct experiment. fi;//<.l - 



ti 'As I have proceeded thus far with these remarks^ it may be 

 considered as equivalent to a retreat from the inquiry to relin- 

 qaiah it in its present stage ; I shall, therefore, add a few other 



