May 26. 1855.] 



NOTES AND QUERIES. 



403 



ceiling, points to the ceiling also on my retina. 

 When I look at St. Paul's Cathedral, and am told 

 that It is inverted on my retina, I find on inquiry 

 that the churchyard, the surrounding buildings, 

 the sky, every object which passes through the 

 lens of the eye, is inverted with the church, and 

 that the relative position of all these objects 

 remains the same ; for the cross which points to 

 the sky in nature, points to the sky on my retina. 

 A stone let fall from the balcony gravitates to the 

 base. The image of the stone does the same on 

 my retina. Here there is no fixed standard by 

 means of which the inversion can be made apparent, 

 nothing, indeed, which will enable us to say with 

 truth that St. Paul's is inverted at all, unless it be 

 so with regard to its absolute position in space, 

 which being purely ideal, is of course imperceptible, 

 and is therefore no measure of the uprightness or 

 inversion of its Image on the retina ; for mere ab- 

 solute position, or direction in space, is altogether 

 beyond the domain of the senses, and may there- 

 fore be regarded (at least so far as the subject of 

 erect vision is concerned) as a nonentity, for 

 " De non apparentibus, et de non existentibus, 

 eadem est ratio." 



If I am told that an object is inverted, and wish 

 to ascertain whether such statement be true or 

 false, I must in the first place seek a fixed, visible, 

 or tangible standard of uprightness, and then 

 compare the object with it. If St. Paul's is in- 

 verted, I naturally ask with respect to what ? 

 Let the standard of uprightness be the ground, 

 and let St. Paul's be said to be upright when the 

 base is on the ground, and the walls make right 

 angles with the churchyard ; then, in order that 

 such statement may be intelligible and true, the 

 building must be placed in the reverse of this 

 position, — the cross must be on the ground, and 

 the base reared up towards the s'sy. If 1 take the 

 houses as a measure, then St. Paul's must be in- 

 verted with respect to them ; but this kind of 

 inversion, which is purely relative, and which pre- 

 supposes the establishment of an immovable and 

 visible standard, is unknown to the retina. There 

 all things occupy the same relative position which 

 they do in nature, for it is clear that on the retina 

 one portion of a landscape is not inverted, while 

 the otliers remain stationary. They are all in- 

 verted pari passu, and the standard or standards 

 of uprightness go along with them. The state- 

 ment then that St. Paul's is inverted on my retina, 

 can have no other meaning than that the cross 

 points In one direiitlon In space, and its image on 

 my retina in the opposite direction; that is, the 

 image is only inverted with respect to the absolute 

 position of the building in space, which, as I have 

 before shown, may be regarded as a nonentity. 

 The representation of nature on the retina may be 

 regarded as our visual world, and it is not more 

 extraordinary that the inversion of this visual 



world should be imperceptible to us, than that our 

 own change of position, occasioned by the daily 

 revolution of the actual world, should be so ; since 

 In both cases our inability to perceive the change 

 arises from the same cause, namely, the absence 

 of a visible standard or measure of position. 



The same reasoning applies equally to the sense 

 of touch, which can only inform us of relative 

 position. A blind man may by touch obtain cor- 

 rect ideas as to the relative position of the fur- 

 niture of his apartment, but can never know by 

 means of this sense the actual position of the 

 various objects in space. He can find out that 

 the legs of his table are upright, that is, that they 

 make right angles with the flogr ; and that the 

 chimney ornaments point to the ceiling, &c. Now 

 If we can conceive the room of this blind man to 

 be turned upside down, and the direction of 

 gravity changed, the sense of touch would convey 

 to the mind the same Ideas as before. The legs of 

 the table would still be felt to be upright, that is, 

 at right angles to the floor, and the chimney or- 

 naments would still be felt to point to the ceiling. 

 Those things which were relatively parallel, at 

 right, acute, or obtuse angles before the inversion, 

 would be so still. Under these circumstances the 

 blind man would certainly be unconscious of his 

 inverted position, for his sense of touch would not 

 inform him of the change which had taken place 

 in his absolute position In space. 



Now since these two senses of sight and touch 

 can only convey to the mind ideas of relative 

 position, and since the relative position of all 

 objects, as indicated by them. Is the same ; and as 

 the retina has of course no secret consciousness of 

 its own position, it follows that there cannot pos- 

 sibly be any discrepancy in their testimony. If I 

 feel that the knob of my walking-stick is against 

 my hand, my sight assures me that I am not mis- 

 taken, for on the retina the image of the knob is 

 against the Imnge of my hand. If I pass my hand 

 along the stick, I feel that It recedes farther and 

 farther from the knob ; my retina announces the 

 same fact, for there also my hand Is passing in 

 the same direction. 



The above observations may be summed up as 

 follows. Sight informs me of the relative position 

 of objects, and nothing more. Touch Informs me 

 of the relative position of objects, and nothlnjg 

 more ; but the relative position of all objects, as 

 indicated by sight, is Identical with their relative 

 position as indicated by touch ; or (leaving ab- 

 solute position out of the question) every object 

 is seen and felt to be in the very same position as 

 it actually occupies In nature. 



In the foregoing attempt at a solution of this 

 vexata qucestio, I do not pretend to have avoided 

 that v.igueness of expression, which is more or 

 less inseparable from popular illustration. I 

 trust, however, that my theory is sufficiently In- 



