1825.] the Seat of Vimn. 261 



mitted./t The effects are therefore the same exactly in their 

 tendency, and have every appearance of arising from the same 

 cause similarly situated; namely, the base of the optic nerve, 

 which is inserted at thie.Mpk of the igye y^xtoV-tJie, ^ngle^i^ 

 question, jdi vd bms ^v/ni/'io blofi arU io oh'l^ fbl ^^ih /JO yy^ 



Although tbe whble of these remarfes'are stated as conclusive 

 evidences of facts, it is by no means intended that no possible^ 

 objection may be urged against the propriety of them, and I am 

 perhaps the more readily induced to make this concession from 

 a knowledge of other peculiar appearances, and which were 

 noticed at the same time that those were observed which have 

 been hitherto the subject of consideration. ■. ;,•.. ;,j£ 



While paying attention to the effect produced by directing 

 my eye towards the moon, on removing the lens from one eye 

 to the other I many times found a dark spot, sometimes sur- 

 rounded with colour, frequently situated near the centre of the 

 nebulous light, but often in other places ; and nothing except 

 the eccentricity of the situations of these spots would have 

 prevented me from placing the spots observed upon the sun's 

 disc by astronomers, to the account of the same illusion of 

 vision. This eccentricity being however considerable, I cannot 

 wholly permit myself to ascribe to a similar deception the 

 spots observed upon the sun, from which its whole phenomena 

 of rotation, and the position of its axis, &c. with regard to the 

 ecliptic has been inferred ; and yet it behoves us to be extremely 

 circumspect in making our deductions in cases where the sub* 

 jects are so continually prolific of deceptions. At tlie same 

 time, however, that this apology for our imperfections is given, 

 I cannot, at present, conceive it possible, that any effects, 

 actually travelhng from the substance of a luminous body like 

 the sun, can be visible to us. So far as the moon is concerned, 

 in which the same forms are always recognised in the same 

 relative places, the probabihties of truth are very different, 

 besides that the characters of the two bodies differ essentially 

 from each other; and it certainly appears evident that nothing 

 less, either than an interposing body between the earth and th^ 

 sun, or, what is highly probable, an illusion of vision similar to 

 the one above-mentioned, could produce the effect of a dark 

 spot on the face of the body in question. If we even admi^ 

 that these spots are openings in the sun's atmosphere, as somi^ 

 have imagined, or that they are chasms in its body, how great 

 must be the extent of these chasms or openings to allow of our 

 discovering them at distances so immense ? Leaving gratuitous 

 assumptions out of the question altogether, however, it will 

 appear evident, on an unprejudiced consideration of the matter, 

 that we can no more discover the surface of the sun with Xh^ 

 best instruments thaYi we can discover with the naked eye, the 

 centre of this earth by iiiealis of a pit, wh(^^e degth^eguaM ^ 

 semi-diameter. . -^ >fju.v r^i i^^, 



